Unit 6 Algebraic Investigations: Quadratics and More, … · Algebraic Investigations: Quadratics and More, ... Mathematics I – Unit 6 Algebraic Investigations: Quadratics and More,

Accelerated Mathematics I

Frameworks

Student Edition

Unit 6

Algebraic Investigations:

Quadratics and More, Part 2

2

nd Edition

March, 2011

Georgia Department of Education

Georgia Department of Education Accelerated Mathematics I Unit 6 2nd Edition


Dr. John D. Barge, State School Superintendent

March, 2011 Page 2 of 32

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Table of Contents

INTRODUCTION: ............................................................................................................ 3

Paula’s Peaches Learning Task: Part 1 .............................................................................. 8

The Protein Bar Toss Learning Task: Part 1 .................................................................... 18

Resistance Learning Task ................................................................................................ 24

Shadows and Shapes Learning Task ................................................................................ 29





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Accelerated Mathematics I – Unit 6

Algebraic Investigations: Quadratics and More, Part 2

Student Edition

INTRODUCTION:

The focus of the unit is developing basic algebra skills and using these in a concentrated study of

quadratic functions and equations. Students will first apply skills developed in Unit 5 in working with

functional models and in solving elementary quadratic, rational, and radical equations. Then, they

extend and apply this basic algebraic knowledge during an in-depth study of quadratics. Students will

learn to solve quadratic equations by applying factoring techniques.

TOPICS

Factoring expressions by greatest common factor, grouping, trial and error, and special products

Operations on rational expressions and solving rational equations

Simplifying expressions and solving simple equations involving square roots

Solving quadratic equations by factoring

ENDURING UNDERSTANDINGS (Units 5, 6, and 7):

Algebraic equations can be identities that express properties of real numbers.

There is an important distinction between solving an equation and solving an applied problem

modeled by an equation. The situation that gave rise to the equation may include restrictions

on the solution to the applied problem that eliminate certain solutions to the equation.

Techniques for solving rational equations include steps that may introduce extraneous solutions

that do not solve the original rational equation and, hence, require an extra step of eliminating

extraneous solutions.

The graph of any quadratic function is a vertical and/or horizontal shift of a vertical stretch or

shrink of the basic quadratic function 2f x x .

The vertex of a quadratic function provides the maximum or minimum output value of the

function and the input at which it occurs. Understand that any equation in can be interpreted as a statement that the values of two

functions are equal, and interpret the solutions of the equation as domain values for the points

of intersection of the graphs of the two functions.

Every quadratic equation can be solved using the Quadratic Formula.

The discriminant of a quadratic equation determines whether the equation has two real roots,

one real root, or two complex conjugate roots.

The complex numbers are an extension of the real number system and have many useful

applications.

The sum of a finite arithmetic series is a quadratic function of the number of terms in the series.





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KEY STANDARDS ADDRESSED:

MA1A1. Students will explore and interpret the characteristics of functions, using graphs,

tables, and simple algebraic techniques.

i. Understand that any equation in x can be interpreted as the equation f(x)=g(x), and interpret the

solutions of the equation as the x-value(s) of the intersection point(s) of the graphs of y = f(x)

and y = g(x).

MA1A2. Students will simplify and operate with radical expressions, polynomials, and rational

expressions. e. Add, subtract, multiply, and divide rational expressions.

f. Factor expressions by greatest common factor, grouping, trial and error, and special products

limited to the formulas below.

2 2 2

2 2 2

2 2

2

3 3 2 2 3

3 3 2 2 3

2

2

3 3

3 3

x y x xy y

x y x xy y

x y x y x y

x a x b x a b x ab

x y x x y xy y

x y x x y xy y

MM1A4. Students will solve quadratic equations and inequalities in one variable.

b. Find real and complex solutions of equations by factoring, taking square roots, and applying

the quadratic formula.

(Unit 3 only addresses finding real solutions of equations by factoring)

RELATED STANDARDS ADDRESSED:

MA1P1. Students will solve problems (using appropriate technology). a. Build new mathematical knowledge through problem solving.

b. Solve problems that arise in mathematics and in other contexts.

c. Apply and adapt a variety of appropriate strategies to solve problems.

d. Monitor and reflect on the process of mathematical problem solving.

MA1P2. Students will reason and evaluate mathematical arguments. a. Recognize reasoning and proof as fundamental aspects of mathematics.

b. Make and investigate mathematical conjectures.

c. Develop and evaluate mathematical arguments and proofs.

d. Select and use various types of reasoning and methods of proof.





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MA1P3. Students will communicate mathematically. a. Organize and consolidate their mathematical thinking through communication.

b. Communicate their mathematical thinking coherently and clearly to peers, teachers, and others.

c. Analyze and evaluate the mathematical thinking and strategies of others.

d. Use the language of mathematics to express mathematical ideas precisely.

MA1P4. Students will make connections among mathematical ideas and to other disciplines. a. Recognize and use connections among mathematical ideas.

b. Understand how mathematical ideas interconnect and build on one another to produce a

coherent whole.

c. Recognize and apply mathematics in contexts outside of mathematics.

MA1P5. Students will represent mathematics in multiple ways. a. Create and use representations to organize, record, and communicate mathematical ideas.

b. Select, apply, and translate among mathematical representations to solve problems.

c. Use representations to model and interpret physical, social, and mathematical phenomena.

UNITS 5, 6, and 7 OVERVIEW

Prior to this unit, students need to have achieved proficiency with the Grade 6 – 8 standards for

Number and Operations, with Grade 8 standards for Algebra, and with the Accelerated Mathematics I

standards addressed in Unit 1 of this course. Tasks in the unit assume an understanding of the

characteristics of functions, especially of the basic function 2f x x and of function transformations

involving vertical shifts, stretches, and shrinks, as well as reflections across the x- and y-axes. As they

work through tasks, students will frequently be required to write mathematical arguments to justify

solutions, conjectures, and conclusions, to apply the Pythagorean Theorem and other concepts related

to polygons, and to draw and interpret graphs in the coordinate plane. They will draw on previous

work with linear inequalities and on their understanding of arithmetic sequences, both in recursive and

closed form.

The initial focus of the unit is developing students’ abilities to perform operations with algebraic

expressions and to use the language of algebra with deep comprehension. In the study of operations on

polynomials, the special products of standard MA1A2 are first studied as product formulas and related

to area models of multiplication. This work lays the foundation for treating these as patterns for

factoring polynomials later in the unit.

The work with rational and radical expressions is grounded in work with real-world contexts and

includes a thorough exploration of the concept of average speed. The need for solving rational

equations is introduced by a topic from physical science, the concept of resistance in an electrical





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circuit; other applications are also included. The presentation focuses on techniques for solving

rational equations and reinforces the topic of solving quadratic equations since rational equations that

lead to both linear and quadratic equations are included. For this unit, the denominators that occur in

the expressions are limited to rational numbers and first degree polynomials. Solution of rational

equations involving higher degree denominators is addressed in Accelerated Mathematics III. (See

standard MA3A1.) Students are also introduced to techniques for solving simple radical equations as

an application of solving equations by finding intersection points of graphs.

Applied problems that can be modeled by quadratic functions or equations are used to introduce and

motivate a thorough exploration of quadratic functions, equations, and inequalities. At first, the

quadratic equations to be solved are limited to those which are equivalent to equations of the form x2 +

bx + c = 0, and students get additional practice in adding, subtracting, and multiplying polynomials as

they put a variety of quadratic equations in this standard form. The study of general quadratic

functions starts with an applied problem that explores horizontal shift transformations and

combinations of this type of transformation with those previously studied. Students work with

quadratic functions that model the behavior of objects that are thrown in the air and allowed to fall

subject to the force of gravity to learn to factor general quadratic expressions completely over the

integers and to solve general quadratic equations by factoring. Student then continue their study of

objects in free fall to learn how to find the vertex of the graph of any polynomial function and to

convert the formula for a quadratic function from standard to vertex form. Next students explore

quadratic inequalities graphically, apply the vertex form of a quadratic function to find real solutions of

quadratic equations that cannot be solved by factoring, and then use exact solutions of quadratic

equations to give exact values for the endpoints of the intervals in the solutions of quadratic

inequalities.

After students have learned to find the real solutions of any quadratic equation, they develop the

concept of the discriminant of a quadratic equation, learn the quadratic formula, and view complex

numbers as non-real solutions of quadratic equations. Students learn to perform basic arithmetic

operations on complex numbers so that they can verify complex solutions to quadratic equations and

can understand that complex solutions exist in conjugate pairs.

The unit ends with an exploration of arithmetic series, the development of formulas for calculating the

sum of such series, and applications of the concepts to counting possible pairs from a set of objects, to

counting the number of diagonals of a polygon, and to understanding the definition of polygonal

numbers.

Algebra is the language used to discuss mathematical applications in business and social science as

well as the natural sciences, computer science, and engineering. Gaining facility with this language is

essential for every educated citizen of the twenty-first century. Throughout this unit, it is important to:

Explain how algebraic expressions, formulas, and equations represent the geometric or physical

situation under consideration.

Find different algebraic expressions for the same quantity and that the verify expressions are

equivalent.





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Make conjectures about mathematical relationships and then give both geometric and algebraic

justifications for the conjecture or use a counterexample to show that the conjecture is false.

Whenever possible, use multiple representations (algebraic, graphical, tabular, and verbal) of

concepts and explain how to translate information from one representation to another.

Use graphing by hand and graphing technology to explore graphs of functions and verify

calculations.

In discussing solutions of equations, put particular techniques for solving quadratic, radical, and

rational equations in the context of the general theory of solving equations.

In the problem solving process, distinguish between solving the equation in the mathematical

model and solving the problem.

As a final note, we observe that completing the square is a topic for Accelerated Mathematics II and is

not used in this unit.

TASKS:

The remaining content of this framework consists of student tasks or activities. The first is intended to

launch the unit. Activities are designed to allow students to build their own algebraic understanding

through exploration. Thorough Teacher’s Guides provide solutions, discuss teaching strategy, and give

additional mathematical background to accompany each task are available to qualified personnel via a

secure web site.





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Paula’s Peaches Learning Task: Part 1

Paula is a peach grower in central Georgia and wants to expand her peach orchard. In her current

orchard, there are 30 trees per acre and the average yield per tree is 600 peaches. Data from the local

agricultural experiment station indicates that if Paula plants more than 30 trees per acre, once the trees

are in production, the average yield of 600 peaches per tree will decrease by 12 peaches for each tree

over 30. She needs to decide how many trees to plant in the new section of the orchard. Throughout

this task assume that, for all peach growers in this area, the average yield is 600 peaches per tree when

30 trees per acre are planted and that this yield will decrease by 12 peaches per tree for each additional

tree per acre.

1. Paula believes that algebra can help her determine the best plan for the new section of orchard and

begins by developing a mathematical model of the relationship between the number of trees per

acre and the average yield in peaches per tree.

a. Is this relationship linear or nonlinear? Explain your reasoning.

b. If Paula plants 6 more trees per acre, what will be the average yield in peaches per tree? What

is the average yield in peaches per tree if she plants 42 trees per acre?

c. Let T be the function for which the input x is the number of trees planted on each acre and T(x)

is the average yield in peaches per tree. Write a formula for T(x) in terms of x and express it in

simplest form. Explain how you know that your formula is correct.

d. Draw a graph of the function T. Given that the information from the agricultural experiment

station applies only to increasing the number of trees per acre, what is an appropriate domain

for the function T?





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2. Since her income from peaches depends on the total number of peaches she produces, Paula

realized that she needed to take a next step and consider the total number of peaches that she can

produce per acre.

a. With the current 30 trees per acre, what is the yield in total peaches per acre? If Paula plants 36

trees per acre, what will be the yield in total peaches per acre? 42 trees per acre?

b. Find the average rate of change of peaches per acre with respect to number of trees per acre

when the number of trees per acre increases from 30 to 36. Write a sentence to explain what

this number means.

c. Find the average rate of change of peaches per acre with respect to the number of trees per acre

when the number of trees per acre increases from 36 to 42. Write a sentence to explain the

meaning of this number.

d. Is the relationship between number of trees per acre and yield in peaches per acre linear?

Explain your reasoning.

e. Let Y be the function that expresses this relationship, that is, the function for which the input x

is the number of trees planted on each acre and the output Y(x) is the total yield in peaches per

acre. Write a formula for Y(x) in terms of x and express your answer in expanded form.

f. Calculate Y(30), Y(36), and Y(42). What is the meaning of these values? How are they related

to your answers to parts a through c?

g. What is the relationship between the domain for the function T and the domain for the function

Y? Explain.





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3. Paula wants to know whether there is a different number of trees per acre that will give the same

yield per acre as the yield when she plants 30 trees per acre.

a. Write an equation that expresses the requirement that x trees per acre yields the same total

number of peaches per acre as planting 30 trees per acre.

b. Use the algebraic rules for creating equivalent equations to obtain an equivalent equation with

an expression in x on one side of the equation and 0 on the other.

c. Multiply this equation by an appropriate rational number so that the new equation is of the form 2 0x bx c . Explain why this new equation has the same solution set as the equations from

parts a and b.

d. When the equation is in the form 2 0x bx c , what are the values of b and c?

e. Find integers m and n such that m n = c and m + n = b.

f. Using the values of m and n found in part e, form the algebraic expression x m x n and

simplify it.

g. Combining parts d through f, rewrite the equation from part c in the form 0x m x n .





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h. This equation expresses the idea that the product of two numbers, x m and x n , is equal to

0. We know from the discussion in Unit 2 that, when the product of two numbers is 0, one of

the numbers has to be 0. This property is called the Zero Factor Property. For these particular

values of m and n, what value of x makes 0x m and what value of x makes 0x n ?

i. Verify that the answers to part h are solutions to the equation written in part a. It is appropriate

to use a calculator for the arithmetic.

j. Write a sentence to explain the meaning of your solutions to the equation in relation to planting

peach trees.

4. Paula saw another peach grower, Sam, from a neighboring county at a farm equipment auction and

began talking to him about the possibilities for the new section of her orchard. Sam was surprised

to learn about the agricultural research and said that it probably explained the drop in yield for a

orchard near him. This peach farm has more than 30 trees per acre and is getting an average total

yield of 14,400 peaches per acre.

a. Write an equation that expresses the situation that x trees per acre results in a total yield per

acre of 14,400 peaches per acre.

b. Use the algebraic rules for creating equivalent equations to obtain an equivalent equation with

an expression in x on one side of the equation and 0 on the other.





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c. Multiply this equation by an appropriate rational number so that the new equation is of the form 2 0x bx c . Explain why this new equation has the same solution set as the equations from

parts a and b.

d. When the equation is in the form2 0x bx c , what is value of b and what is the value of c?

e. Find integers m and n such that m n = c and m + n = b .

f. Using the values of m and n found in part e, form the algebraic expression x m x n and

simplify it.

g. Combining parts d through f, rewrite the equation from part d in the form 0x m x n .

h. This equation expresses the idea that the product of two numbers, x m and x n , is equal to 0.

We know from the discussion in Unit 2 that, when the product of two numbers is 0, one of the

numbers has to be 0. What value of x makes 0x m ? What value of x makes 0x n ?

i. Verify that the answers to part h are solutions to the equation written in part a. It is appropriate

to use a calculator for the arithmetic.

j. Which of the solutions verified in part i is (are) in the domain of the function Y? How many

peach trees per acre are planted at the peach orchard getting 14400 peaches per acre?





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The steps in items 3 and 4 outline a method of solving equations of the form 2 0x bx c . These

equations are called quadratic equations and an expression of the form 2x bx c is called a

quadratic expression. In general, quadratic expressions may have any nonzero coefficient on the 2x term, but in Mathematics I we focus on quadratic expressions with coefficient 1 on the 2x term. An

important part of this method for solving quadratic equations is the process of rewriting an expression

of the form 2x bx c in the form x m x n . The rewriting step is an application of Identity 1

from Unit 2. The identity tells us that the product of the numbers m and n must equal c and that the

sum of m and n must equal b. In Mathematics I, we will apply Identity 1 in this way only when the

values of b, c, m, and n are integers.

5. Since the whole expression x m x n is a product, we call the expressions x m and x n

the factors of this product. For the following expressions in the form 2x bx c , rewrite the

expression as a product of factors of the form x + m and x + n. Verify each answer by drawing a

rectangle with sides of length x m and x n , respectively, and showing geometrically that the

area of the rectangle is 2x bx c .

a. 2 3 2x x

b. 2 6 5x x

c. 2 5 6x x

d. 2 7 12x x

e. 2 8 12x x

f. 2 13 36x x

g. 2 13 12x x

6. In item 5, the values of b and c were positive. Now use Identity 1 in reverse to factor each of the

following quadratic expressions of the form 2x bx c where c is positive but b is negative.

Verify each answer by multiplying the factored form to obtain the original expression.

a. 2 8 7x x

b. 2 9 18x x

c. 2 4 4x x

d. 2 8 15x x

e. 2 11 24x x

f. 2 11 18x x

g. 2 12 27x x





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7. Use Identity 1 in reverse to factor each of the following quadratic expressions of the form 2x bx c where c is negative. Verify each answer by multiplying the factored form to obtain the

original expression.

a. 2 6 7x x

b. 2 6 7x x

c. 2 42x x

d. 2 42x x

e. 2 10 24x x

f. 2 10 24x x

8. In items 3 and 4, we used factoring as part of a process to solve equations that are equivalent to

equations of the form 2 0x bx c where b and c are integers. Look back at the steps you did in

items 3 and 4, and describe the process for solving an equation of the form 2 0x bx c . Use

this process to solve each of the following equations, that is, to find all of the numbers that satisfy

the original equation. Verify your work by checking each solution in the original equation.

a. 2 6 8 0x x

b. 2 15 36 0x x

c. 2 28 27 0x x

d. 2 3 10 0x x

e. 2 2 15 0x x

f. 2 4 21 0x x

g. x2 – 7x = 0

h. 2 13 0x x





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9. The process you used in item 8 works whenever you have an equation in the form 2 0x bx c .

There are many equations, like those in items 3 and 4, that look somewhat different from this form

but are, in fact, equivalent to an equation in this form. Remember that the Addition Property of

Equality allows us to get an equivalent equation by adding the same expression to both sides of the

equation and the Multiplicative Property of Equality allows us to get an equivalent equation by

multiplying both sides of the equation by the same number as long as the number we use is not 0.

For each equation below, find an equivalent equation in the form 2 0x bx c .

a. 26 12 48 0x x

b. 2 8 9x x

c. 23 21 30x x

d. 24 24 20x x

e. 11 30 0x x

f. 1

8 102

x x

g. 1 5 3 0x x

h. 2

5 49x

i. 2 3 4 24x x x

j. 5 3 200x x

10. Now we return to the peach growers in central Georgia. How many peach trees per acre

would result in only 8400 peaches per acre?

11. If there are no peach trees on a property, then the yield is zero peaches per acre. Write an

equation to express the idea that the yield is zero peaches per acre with x trees planted per

acre, where x is number greater than 30. Is there a solution to this equation, that is, is there a

number of trees per acre that is more than 30 and yet results in a yield of zero peaches per

acre? Explain.





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12. At the same auction where Paula heard about the peach grower who was getting a low yield,

she talked to the owner of a major farm supply store in the area. Paula began telling the store

owner about her plans to expand her orchard, and the store owner responded by telling her

about a local grower that gets 19,200 peaches per acre. Is this number of peaches per acre

possible? If so, how many trees were planted?

13. Using graph paper, explore the graph of Y as a function of x.

a. What points on the graph correspond to the answers for part j from items 3and 4?

b. What points on the graph correspond to the answers to items 10, 11, and 12?

c. What is the relationship of the graph of the function Y to the graph of the function f ,

where the formula for f(x) is the same as the formula for Y(x) but the domain for f is all

real numbers?

d. Items 4, 10, and 11 give information about points that are on the graph of f but not on the

graph of Y. What points are these?

e. Graph the functions f and Y on the same axes. How does your graph show that the

domain of f is all real numbers? How is the domain of Y shown on your graph?





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14. In answering parts a, b, and d of item 13, you gave one geometric interpretation of the

solutions of the equations solved in items 3, 4, 10, 11, and 12. We now explore a slightly

different viewpoint.

a. Draw the line y = 18000 on the graph drawn for item 13, part e. This line is the graph of

the function with constant value 18000. Where does this line intersect the graph of the

function Y? Based on the graph, how many trees per acre give a yield of more than

18000 peaches per acre?

Draw the line y = 8400 on your graph. Where does this line intersect the graph of the

function Y? Based on the graph, how many trees per acre give a yield of fewer than 8400

peaches per acre?

b. Use a graphing utility and this intersection method to find the number of trees per acre

that give a total yield closest to the following numbers of peaches per acre:

(i) 10000 (ii) 15000

(iii) 20000

c. Find the value of the function Y for the number of trees given in answering (i) – (iii) in

part c above.

15. For each of the equations solved in item 8, do the following.

a. Use technology to graph a function whose formula is given by the left-hand side of the

equation.

b. Find the points on the graph which correspond to the solutions found in item 8.

c. How is each of these results an example of the intersection method explored in item 14?





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The Protein Bar Toss Learning Task: Part 1

Blake and Zoe were hiking in a wilderness area. They came up to a scenic view at the edge of a

cliff. As they stood enjoying the view, Zoe asked Blake if he still had some protein bars left,

and, if so, could she have one. Blake said, “Here’s one; catch!” As he said this, he pulled a

protein bar out of his backpack and threw it up to toss it to Zoe. But the bar slipped out of his

hand sooner than he intended, and the bar went straight up in the air with his arm out over the

edge of the cliff. The protein bar left Blake’s hand moving straight up at a speed of 24 feet per

second. If we let t represent the number of seconds since the protein bar left the Blake’s hand

and let h(t) denote the height of the bar, in feet above the ground at the base of the cliff, then,

assuming that we can ignore the air resistance, we have the following formula expressing h(t) as

a function of t,

2( ) 16 24 160h t t t .

In this formula, the coefficient on the 2t -term is due to the effect of gravity and the coefficient

on the t-term is due to the initial speed of the protein bar caused by Blake’s throw. In this task,

you will explore, among many things, the source of the constant term.

1. In part 5 of Exploring Functions with Fiona , from Unit 1, you considered a formula for the

distance fallen by an object dropped from a high place. List some ways in which this

situation with Blake and the protein bar differs from the situation previously studied.

2. Use technology to graph the equation 216 24 160y t t . Find a viewing window that

includes the part of this graph that corresponds to the situation with Blake and his toss of the

protein bar. What viewing window did you select?

3. What was the height of the protein bar, measured from the ground at the base of the cliff, at

the instant that it left Blake’s hand? What special point on the graph is associated with this

information?

4. If Blake wants to reach out and catch the protein bar on its way down, how many seconds

does he have to process what happened and position himself to catch it? Justify your answer

graphically and algebraically.





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5. If Blake does not catch the falling protein bar, how long it take for the protein bar to hit the

ground below the cliff? Justify your answer graphically. Then write a quadratic equation

that you would need to solve to justify the answer algebraically.

The equation from item 5 can be solved by factoring, but it requires factoring a quadratic

polynomial where the coefficient of the x2-term is not 1. Our next goal is to learn about factoring

this type of polynomial. We start by examining products that lead to such quadratic

polynomials.

6. For each of the following, perform the indicated multiplication and use a rectangular model

to show a geometric interpretation of the product as area for positive values of x.

a. 2 3 3 4x x

b. 2 4 11x x

c. 2 1 5 4x x

7. For each of the following, perform the indicated multiplication.

a. 2 3 9 2x x

b. 3 1 4x x

c. 4 7 2 9x x





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The method for factoring general quadratic polynomial of the form 2ax bx c , with a, b, and c

all non-zero integers, is similar to the method learned in Mathematics I for factoring quadratics

of this form but with the value of a restricted to a = 1. The next item guides you through an

example of this method.

8. Factor the quadratic polynomial 26 7 20x x using the following steps.

a. Think of the polynomial as fitting the form 2ax bx c .

What is a? ____ What is c? ____ What is the product ac? ____

b. List all possible pairs of integers such that their product is equal to the number ac. It may

be helpful to organize your list in a table. Make sure that your integers are chosen so that

their product has the same sign, positive or negative, as the number ac from above, and

make sure that you list all of the possibilities.

c. What is b in the quadratic polynomial given? _____ Add the integers from each pair

listed in part b. Which pair adds to the value of b from your quadratic polynomial?

We’ll refer to the integers from this pair as m and n.

d. Rewrite the polynomial replacing bx with mx nx . [Note either m or n could be

negative; the expression indicates to add the terms mx and nx including the correct sign.]

e. Factor the polynomial from part d by grouping.

f. Check your answer by performing the indicated multiplication in your factored

polynomial. Did you get the original polynomial back?





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9. Use the method outlined in the steps of item 8 to factor each of the following quadratic

polynomials. Is it necessary to always list all of the integer pairs whose produst is ac?

a. 2x2 + 3x – 54

b. 4w2 -11w + 6

c. 3t2 -13t – 10

d. 8x2 + 5x – 3

e. 18z2 +17z + 4

f. 6p2 – 49p + 8

Use the method outlined in the steps of item 8 to factor each of the following quadratic

polynomials. Is it necessary to always list all of the integer pairs whose product is ac? Explain

your answer

10. If you are reading this, then you should have factored all of the quadratic polynomials listed

in item 9 in the form Ax B Cx D , where the A, B, C, and D are all integers.

a. Compare your answers with other students, or other groups of students. Did everyone in

the class write their answers in the same way? Explain how answers can look different

but be equivalent.

b. Factor 224 4 8q q completely.

c. Show that 224 4 8q q can be factored in the form Ax B Cx D , where the A, B,

C, and D are all integers, using three different pairs of factors.

d. How should answers to quadratic factoring questions be expressed so that everyone who

works the problem correctly lists the same factors, just maybe not in the same order?





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11. If a quadratic polynomial can be factored in the form Ax B Cx D , where the A, B, C,

and D are all integers, the method you have been using will lead to the answer, specifically

called the correct factorization. As you continue your study of mathematics, you will learn

ways to factor quadratic polynomials using numbers other than integers. For right now,

however, we are interested in factors that use integer coefficients. Show that each of the

quadratic polynomials below cannot be factored in the form Ax B Cx D , where the A,

B, C, and D are all integers.

a. 24 6z z

b. 2 2 8t t

c. 23 15 12x x

12. Now we return to our goal of solving the equation from item 5. Recall that you solved

quadratic equations of the form 2 0ax bx c , with a = 1, in Mathematics I. The method

required factoring the quadratic polynomial and using the Zero Factor Property. The same

method still applies when 1a , its just that the factoring is more involved, as we have seen

above. Use your factorizations from items 9 and 10 as you solve the quadratic equations

below.

a. 22 3 54 0x x

b. 24 6 11w w

c. 23 13 10t t

d. 2 4 3 3x x x

e. 218 21 4 1z z z

f. 8 13 6 6p p p

g. 224 4 8q q

13. Solve the quadratic equation from item 5. Explain how the solution gives an algebraic

justification for your answer to the question.





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14. Suppose the cliff had been 56 feet higher. Answer the following questions for this higher

cliff.

a. What was the height of the protein bar, measured from the ground at the base of the cliff,

at the instant that it left Blake’s hand? What special point on the graph is associated with

this information?

b. What is the formula for the height function in this situation?

c. If Blake wants to reach out and catch the protein bar on its way down, how many seconds

does he have to process what has happened and position himself to catch it? Justify your

answer algebraically.

d. If Blake does not catch the falling protein bar, how long it take for the protein bar to hit

the ground below the cliff? Justify your answer algebraically.

15. Suppose the cliff had been 88 feet lower. Answer the following questions for this lower cliff.

.

a. What was the height of the protein bar, measured from the ground at the base of the cliff,

at the instant that it left Blake’s hand? What special point on the graph is associated with

this information?

b. What is the formula for the height function in this situation?

c. If Blake wants to reach out and catch the protein bar on its way down, how many seconds

does he have to process what has happened and position himself to catch it? Justify your

answer algebraically.

d. If Blake does not catch the falling protein bar, how long it take for the protein bar to hit

the ground below the cliff? Justify your answer algebraically.





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Notes on Resistance Learning Task

We use electricity every day to do everything from brushing our teeth to powering our

cars. Electricity results from the presence and flow of electric charges. Electrons with a

negative charge are attracted to those with a positive charge. Electrons cannot travel

through the air. They need a path to move from one charge to the other. This path is called

a circuit. A simple circuit can be seen in the connection of the negative and positive ends of

a battery.

When a circuit is created, electrons begin moving from the one charge to the other. In the

circuit below, a bulb is added to the circuit. The electrons pass through the filament in the

bulb heating it and causing it to glow and give off light.

Electrons try to move as quickly as possible. If a circuit is not set up carefully, too many

electrons can move across at one time causing the circuit to break. We can limit the

number of electrons crossing over a circuit to protect it. Adding objects that use electricity,

such as the bulb in the above circuit, is one way to limit the flow of electrons. This limiting

of the flow of electrons is called resistance. It is often necessary to add objects called

resistors to protect the circuit and the objects using the electricity passing through the

circuit. In the circuit below, R1 represents a resistor.

More than one resistor can be placed on a circuit. The placement of the resistors

determines the total effect on the circuit. The resistors in the diagram below are placed in

parallel (this refers to the fact that there are no resistors directly between two resistors, not

to the geometric definition of parallel). Parallel resistors allow multiple paths for the

electricity to flow. Two examples of parallel resistors are shown below.





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The resistors in the next circuit below are not parallel. These resistors are placed in series

because the electricity must travel through all three resistors as it travels through the circuit.

Resistance is measured in units called ohms and must always be a positive number. The omega

symbol, Ω, is used to represent ohms.

For n resistors in parallel, R1, R2, R3, etc. the total resistance, RT, across a circuit can be found

using the equation:

1 2 3

1 1 1 1 1

T nR R R R R

For n resistors is series, R1, R2, R3, etc. the total resistance, RT, across a circuit can be found

using the equation:

1 2 3T nR R R R R





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1. What is the total resistance for a circuit with three resistors in series if the resistances are 2

ohms, 5 ohms, and 4 ohms, respectively?

2. What is the total resistance for a circuit with two parallel resistors, one with a resistance of 3

ohms and the other with a resistance of 7 ohms?

3. What is the total resistance for a circuit with four resistors in parallel if the resistances are 1

ohm, 3 ohms, 5

2ohms, and

3

5ohms, respectively?

4. What is the total resistance for the circuit to

the right?

5. A circuit with a total resistance of 28

11 has two parallel resistors. One of the resistors has a

resistance of 4 ohms.

a. Let x represent the resistance of the other of the other resistor, and write an equation for

the total resistance of the circuit.

b. The equation in part a contains rational expressions. If you have any complex fractions,

simplify them. In your equation containing no complex fractions, what is the least

common denominator of the rational expressions?





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c. Use the Multiplication Principle of Equality to obtain a new equation that has the same

solutions as the equation in part a but does not contain any rational expressions. Why do

you know that x ≠ 0? How does knowing that x ≠ 0 allow you to conclude that this new

equation has the same solutions as, or is equivalent to, the equation from part a.

d. Solve the new equation to find the resistance in the second resistor. Check your answer.

6. A circuit has been built using two parallel resistors.

a. One resistor has twice the resistance of the other. If the total resistance of the circuit is

3

4 ohms, what is the resistance of each of the two resistors?

b. One resistor has a resistance of 4 ohms. If the total resistance is one-third of that of the

other parallel resistor, what is the total resistance?

7. A circuit has been built using two paths for the flow of the current;

one of the paths has a single resistor and the other has two resistors

in series as shown in the diagram at the right.

a. Assume that, for the two resistors in series, the second has a

resistance that is three times the resistance of the first one in the

series. The single resistor has a resistance that is 6 ohms more than

the resistance of the first resistor in series, and the total resistance

of the circuit is 4 Ω. Write an equation to model this situation, and

solve this equation. What is the solution set of the equation? What

is the resistance of the each of the resistors?

b. Assume that, for the two resistors in series, the second has a resistance that is 3 ohms

more than twice the resistance of the first one in the series. The single resistor has a

resistance that is 1 ohm more than the resistance of the first resistor in series, and the

total resistance of the circuit is 3 Ω. Write an equation to model this situation, and solve

this equation. What is the solution set of the equation? What is the resistance of the

each of the resistors?





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c. Assume that, for the two resistors in series, the second has a resistance that is 2 ohms

more than the first one in the series. The single resistor has a resistance that is 3 ohms

more than the resistance of the first resistor in series, and the total resistance of the

circuit is 2 Ω. Write an equation to model this situation, and solve this equation. What

is the solution set of the equation? What is the resistance of the each of the resistors?

d. Assume that, for the two resistors in series, the second has a resistance that is 4 ohms

more than the first one in the series. The single resistor has a resistance that is 3 ohms

less than the resistance of the first resistor in series, and the total resistance of the circuit

is 4 Ω. . Write an equation to model this situation, and solve this equation. What is the

solution set of the equation? What is the resistance of the each of the resistors?

8. A circuit has three resistors in parallel. The second resistor has a resistance that is 4 ohms

more than the first. The third resistor has a resistance of 8 ohms. The total resistance is one-

half the resistance of the first resistor. Find each of the unknown resistances.





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Shadows and Shapes Learning Task

1. At a particular time one spring day in a park area with level ground, a pine tree casts a 60-

foot shadow while a nearby post that is 5 feet high casts an 8-foot shadow.

a. Using the figure below, draw appropriate lines to indicate the rays of sunlight which are

always parallel.

b. Let h represent the height of the pine tree. Use relationships about similar triangles to

write an equation involving h.

c. Find the height of the pine tree, to the nearest foot.





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2. On bright sunny day, two men are standing in an open plaza. The shorter man is wearing a

hat that makes him appear to be the same height as the other man, who is not wearing a hat.

The hat is designed so that the top of the hat is 4 inches above the top of the wearer’s head.

When the shorter man takes off his hat, he casts a 51-inch shadow while the taller man casts

a 54-inch shadow. How tall is each man?

3. The plaza floor has a geometric design. The design includes

similar right triangles with the relationships shown in the

figure at the right.

a. If the hypotenuse of the larger right triangle is 15 inches,

what is the length of the other hypotenuse? Explain why.

b. Assuming the hypotenuse of the larger right triangle is 15

inches, for each triangle, write an equation expressing a

relationship among the lengths of the sides of the triangle.

c. Solve at least one of the equations from part b, and find the

lengths of the legs of both triangles.

4. Another shape in the plaza floor design is a right triangle with hypotenuse 26-inches long and

one leg 24 inches long.

a. Let x denote the length of the other leg of this triangle. Write a quadratic equation

expressing a relationship among the lengths of the sides of the triangle.

b. Put this equation in the standard form 2 0x bx c . What are the values of b and c?

c. What is the length of the other leg of the triangle?





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5. When you put the equation you solved in item 4 in standard form, you were working with an

equation in the form2 0x c . In item 4, the value of c is a perfect square, so you could

use the Difference of Square identity to solve the equation by factoring. Use this identity and

factoring to solve each of the equations below, each of which has the form 2 0x c .

a. 2 25 0x

b. 2 49 0x

c. 2 4 0x

d. 2 81 0x

e. 2 121 0x

f. 2 64 0x

5. Make a quick sketch of the graphs of each of the functions listed below, and discuss how the

solutions from item 5 can be seen in the graphs.

a. 2 25f x x

b. 2 49f x x

c. 2 4f x x

d. 2 81f x x

e. 2 121f x x

f. 2 64f x x

6. Use the graphs of appropriate functions to solve each of the following equations.

a. 2 5 0x

b. 2 11 0x

c. 2 5 0x

d. 2 8 0x

e. 2 2 0x

f. 2 12 0x





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g. Explain why each equation has two solutions.

h. For a quadratic equation of the form 2 0x c with 0c , how many solutions does the

equation have? In terms of c, what are the solutions?

7. In the figure at the right, a line has been added to the part of the design from item 3. As

shown, the shorter leg of the smaller right triangle and the longer leg of the larger right

triangle form the legs of this new right triangle.

a. Let z represent the length of the hypotenuse of this new right triangle, as indicated. Use

the Pythagorean Theorem, and the lengths you found in item 3 to find z.

b. If a line segment were drawn from point A to point B in the figure, what would be the

length of the segment?

Unit 6 Algebraic Investigations: Quadratics and More, … · Algebraic Investigations: Quadratics and More, ... Mathematics I – Unit 6 Algebraic Investigations: Quadratics and More,

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