A. 17.9 B. 22 C. 13.3 D. 9.1 Find the perimeter of quadrilateral WXYZ with vertices W(2, 4), X(–3, 3), Y(–1, 0), and Z(3, –1).
Feb 23, 2016
A. 17.9
B. 22
C. 13.3
D. 9.1
Find the perimeter of quadrilateral WXYZ with verticesW(2, 4), X(–3, 3), Y(–1, 0), and Z(3, –1).
Unit 1-Lesson 4
Area of two dimensional figures
Objective
• I can recall area formulas for parallelograms, trapezoids, and triangles
Before Area…
• We need to recall some important mathematical tools
• Pythagorean Theorem
• Right Angles / Triangles
Right Angles
• Right angles measure 90 degrees• Two segments / lines that form a right angle are
perpendicular
This symbol indicates a right angle
Right Triangle
• A right triangle has exactly one right angle
Can you find the right triangles?
A Right Triangle’s Best Friend
• The Pythagorean Theorem
• A2 + B2 = C2
• The sum of the squares of the legs of a right triangle is equal to the square of its hypotenuse
ExamplePythagorean Theorem
• Find the value of x
x
15
6
A = 6 B = 15 C = x
62 + 152 = x2
36 + 225 = x2
261 = x2
x = 261 293
Why?
• In order to find surface area, you need to use know the height of the figure
• Height – perpendicular distance (you will see a right angle)
Area of a Parallelogram
Area of a Parallelogram
• Be careful!
height
Base
Yes! Notice the height intersects the base
heightBaseNO! Base and
height do not intersect at a right angle
Area of a Parallelogram
Find the area of
Area of a Parallelogram
Area Find the height of the parallelogram. The height forms a right triangle with points S and T with base 12 in. and hypotenuse 20 in.
c2 = a2 + b2 Pythagorean Theorem
202 = 122 + b2 c = 20 and a = 12
400 = 144 + b2 Simplify.
256 = b2 Subtract 144 from each side.
16 = b Take the square root of each side.
Area of a Parallelogram
Continued
A = bh Area of parallelogram
= (32)(16) or 512 in2 b = 32 and h = 16
The height is 16 in. UT is the base, which measures 32 in.
Answer: The area is 512 in2.
A. AB. BC. CD. D
A. 88 m; 255 m2
B. 88 m; 405 m2
C. 88 m; 459 m2
D. 96 m; 459 m2
A. Find the perimeter and area of
Area of a Triangle
Application
Perimeter and Area of a Triangle
SANDBOX You need to buy enough boards to make the frame of the triangular sandbox shown and enough sand to fill it. If one board is 3 feet long and one bag of sand fills 9 square feet of the sandbox, how many boards and bags do you need to buy?
What is it asking for?
Application
Perimeter and Area of a TriangleStep 1 Find the perimeter of the sandbox.
Perimeter = 16 + 12 + 7.5 or 35.5 ft
Step 2 Find the area of the sandbox.
Area of a triangle
b = 12 and h = 9
Application
Perimeter and Area of a Triangle
Step 3 Use unit analysis to determine how many ofeach item are needed.
Boards
Bags of Sand
boards
Answer: You will need 12 boards and 6 bags of sand.
Area of a Trapezoid
Area of a Trapezoid
SHAVING Find the area of steel used to make
the side of the trapezoid shown below.
Area of a trapezoid
h = 1, b1 = 3, b2 = 2.5
Simplify.
Answer: A = 2.75 cm2
Area of a Trapezoid
OPEN ENDED Miguel designed a deck shaped like the trapezoid shown below. Find the area of the deck.
Read the Problem
You are given a trapezoid with one base measuring 4 feet, a height of 9 feet, and a third side measuring 5 feet. To find the area of the trapezoid, first find the measure of the other base.
Solve the Test Item
Draw a segment to form a right triangle and a rectangle. The triangle has a hypotenuse of 5 feet and legs of ℓ and 4 feet. The rectangle has a length of 4 feet and a width of x feet.
Use the Pythagorean Theorem to find ℓ.
a2 + b2 = c2 Pythagorean Theorem42 + ℓ2 = 52 Substitution
16 + ℓ2 = 25 Simplify.ℓ2 = 9 Subtract 16 from each side.ℓ = 3 Take the positive square root
of each side.
By Segment Addition, ℓ + x = 9. So, 3 + x = 9 and x = 6. The width of the rectangle is also the measure of the second base of the trapezoid.
Area of a trapezoid
Substitution
Simplify.Answer: So, the area of the deck is 30 square feet.
Area of a Rhombus or Kite
The area A of a rhombus or a kite is one half the product of the length of its diagonals, d1 and d2
A= d1d2
25
12
26
Area of Regions
8
10
12
4 14
8
The area of a region is the sum of all of its non-overlapping parts.
A = ½(8)(10)
A= 40A = (12)(10)
A= 120
A = (4)(8)
A=32
A = (14)(8)
A=112
Area = 40 + 120 + 32 + 112 = 304 sq. units
Other Types of Polygons
• Regular Polygon – a polygon with sides that are all the same length and angles that are all the same measure
28
Areas of Regular Polygons
Perimeter = (6)(8) = 48 apothem =
Area = ½ (48)( ) = sq. units
8
If a regular polygon has an area of A square units, a perimeter of P units, and an apothem of a units, then A = ½ (a)(p).
4 34 3
4 3 96 3