Lesson 6-5 Multiplying Polynomials · 2018. 9. 4. · Holt McDougal Algebra 1 6-5 Multiplying Polynomials To multiply monomials and polynomials, you will use some of the properties

Holt McDougal Algebra 1

6-5 Multiplying Polynomials6-5 Multiplying Polynomials

Holt Algebra 1

Warm Up

Lesson Presentation

Lesson Quiz



6-5 Multiplying Polynomials

Warm UpEvaluate.

1. 32

3. 102

Simplify.

4. 23 • 24

6. (53)2

9 16

100

27

2. 24

5. y5 • y4

56 7. (x2)4

8. –4(x – 7) –4x + 28

y9

x8



Multiply polynomials.

Objective



To multiply monomials and polynomials, you will use some of the properties of exponents that you learned earlier in this chapter.



Multiply.

Example 1: Multiplying Monomials

A. (6y3)(3y5)

(6y3)(3y5)

18y8

Group factors with like bases

together.

B. (3mn2) (9m2n)

(3mn2)(9m2n)

27m3n3

Multiply.


together.

Multiply.

(6 3)(y3 y5)••••••••

(3 9)(m m2)(n2 • n)••••••••



Multiply.

Example 1C: Multiplying Monomials

−−−−4 53s t

Group factors with like

bases together.

Multiply.

(((( ))))(((( ))))

−−−−22 21

124

ts tt s s

(((( ))))(((( ))))••

•

2 21−12

4ts ts ts

2• •

14 s2 t2 (st) (-12 s t2)



When multiplying powers with the same base, keep the base and add the exponents.

x2 •••• x3 = x2+3 = x5

Remember!



Check It Out! Example 1

Multiply.

a. (3x3)(6x2)

(3x3)(6x2)

(3 6)(x3 x2)••••••••

18x5


together.

Multiply.


together.

Multiply.

b. (2r2t)(5t3)

(2r2t)(5t3)

(2 5)(r2)(t3 t)••••••••

10r2t4



Check It Out! Example 1 Continued

Multiply.

Group factors with

like bases

together.

Multiply.

c.

(((( ))))(((( ))))

4 52 2112

3x zy zx y

3

(((( ))))(((( ))))

2112

3x y x z y z

2 4 53

(((( ))))(((( ))))(((( ))))

3 22 4 5112 z

3zx x y y

7554x y z

• • • •



To multiply a polynomial by a monomial, use the Distributive Property.



Multiply.

Example 2A: Multiplying a Polynomial by a Monomial

4(3x2 + 4x – 8)

4(3x2 + 4x – 8)

(4)3x2 +(4)4x – (4)8

12x2 + 16x – 32

Multiply.

Distribute 4.



6pq(2p – q)

(6pq)(2p – q)

Multiply.

Example 2B: Multiplying a Polynomial by a Monomial

(6pq)2p + (6pq)(–q)

(6 •••• 2)(p •••• p)(q) + (–1)(6)(p)(q • q)

12p2q – 6pq2

Group like bases

together.

Multiply.

Distribute 6pq.



Multiply.

Example 2C: Multiplying a Polynomial by a Monomial

Group like bases

together.

Multiply.

(((( ))))++++21

62

x y xy x y82 2

x y(((( ))))++++22 6

1

2xyyx 8

2

x y x y(((( )))) (((( ))))

++++2 21

62

8xy x y 22

1

2

x2 • x(((( ))))(((( )))) (((( ))))(((( ))))

++++

1• 6

2y • y x2 • x2 y • y2• 8

1

2

3x3y2 + 4x4y3

Distribute .21x y

2




Multiply.

a. 2(4x2 + x + 3)

2(4x2 + x + 3)

2(4x2) + 2(x) + 2(3)

8x2 + 2x + 6

Multiply.

Distribute 2.




Multiply.

b. 3ab(5a2 + b)

3ab(5a2 + b)

(3ab)(5a2) + (3ab)(b)

(3 • 5)(a • a2)(b) + (3)(a)(b • b)

15a3b + 3ab2

Group like bases

together.

Multiply.

Distribute 3ab.




Multiply.

c. 5r2s2(r – 3s)

5r2s2(r – 3s)

(5r2s2)(r) – (5r2s2)(3s)

(5)(r2 • r)(s2) – (5 • 3)(r2)(s2 • s)

5r3s2 – 15r2s3

Group like bases

together.

Multiply.

Distribute 5r2s2.



To multiply a binomial by a binomial, you can apply the Distributive Property more than once:

(x + 3)(x + 2) = x(x + 2) + 3(x + 2)

Multiply.

Combine like terms.

= x(x + 2) + 3(x + 2)

= x(x) + x(2) + 3(x) + 3(2)

= x2 + 2x + 3x + 6

= x2 + 5x + 6

Distribute.

Distribute again.



Another method for multiplying binomials is called the FOIL method.

4. Multiply the Last terms. (x + 3)(x + 2) 3 2 = 6••••

3. Multiply the Inner terms. (x + 3)(x + 2) 3 x = 3x••••

2. Multiply the Outer terms. (x + 3)(x + 2) x 2 = 2x••••

F

O

I

L

(x + 3)(x + 2) = x2 + 2x + 3x + 6 = x2 + 5x + 6

F O I L

1. Multiply the First terms. (x + 3)(x + 2) x x = x2••••



Multiply.

Example 3A: Multiplying Binomials

(s + 4)(s – 2)

(s + 4)(s – 2)

s(s – 2) + 4(s – 2)

s(s) + s(–2) + 4(s) + 4(–2)

s2 – 2s + 4s – 8

s2 + 2s – 8

Distribute.

Distribute again.

Multiply.

Combine like terms.



Multiply.

Example 3B: Multiplying Binomials

(x – 4)2

(x – 4)(x – 4)

(x x) + (x (–4)) + (–4 • x) + (–4 • (–4))••••••••

x2 – 4x – 4x + 16

x2 – 8x + 16

Write as a product of

two binomials.

Use the FOIL method.

Multiply.

Combine like terms.



Example 3C: Multiplying Binomials

Multiply.

(8m2 – n)(m2 – 3n)

8m2(m2) + 8m2(–3n) – n(m2) – n(–3n)

8m4 – 24m2n – m2n + 3n2

8m4 – 25m2n + 3n2


Multiply.

Combine like terms.



In the expression (x + 5)2, the base is (x + 5). (x + 5)2 = (x + 5)(x + 5)

Helpful Hint



Check It Out! Example 3a

Multiply.

(a + 3)(a – 4)

(a + 3)(a – 4)

a(a – 4)+3(a – 4)

a(a) + a(–4) + 3(a) + 3(–4)

a2 – a – 12

a2 – 4a + 3a – 12

Distribute.

Distribute again.

Multiply.

Combine like terms.



Check It Out! Example 3b

Multiply.

(x – 3)2

(x – 3)(x – 3)

(x x) + (x•(–3)) + (–3 • x)+ (–3)(–3)●

x2 – 3x – 3x + 9

x2 – 6x + 9

Write as a product of

two binomials.


Multiply.

Combine like terms.



Check It Out! Example 3c

Multiply.

(2a – b2)(a + 4b2)

(2a – b2)(a + 4b2)

2a(a) + 2a(4b2) – b2(a) + (–b2)(4b2)

2a2 + 8ab2 – ab2 – 4b4

2a2 + 7ab2 – 4b4


Multiply.

Combine like terms.



To multiply polynomials with more than two terms, you can use the Distributive Property several times. Multiply (5x + 3) by (2x2 + 10x – 6):

(5x + 3)(2x2 + 10x – 6) = 5x(2x2 + 10x – 6) + 3(2x2 + 10x – 6)

= 5x(2x2 + 10x – 6) + 3(2x2 + 10x – 6)

= 5x(2x2) + 5x(10x) + 5x(–6) + 3(2x2) + 3(10x) + 3(–6)

= 10x3 + 50x2 – 30x + 6x2 + 30x – 18

= 10x3 + 56x2 – 18



You can also use a rectangle model to multiply polynomials with more than two terms. This is similar to finding the area of a rectangle with length (2x2 + 10x – 6) and width (5x + 3):

2x2 +10x –6

10x3 50x2 –30x

30x6x2 –18

5x

+3

Write the product of the

monomials in each row and

column:

To find the product, add all of the terms inside the rectangle by combining like terms and simplifying if necessary.

10x3 + 6x2 + 50x2 + 30x – 30x – 18

10x3 + 56x2 – 18



Another method that can be used to multiply polynomials with more than two terms is the vertical method. This is similar to methods used to multiply whole numbers.

2x2 + 10x – 6

5x + 3××××

6x2 + 30x – 18

+ 10x3 + 50x2 – 30x

10x3 + 56x2 + 0x – 18

10x3 + 56x2 + – 18

Multiply each term in the top

polynomial by 3.

Multiply each term in the top

polynomial by 5x, and align

like terms.

Combine like terms by adding

vertically.

Simplify.



Multiply.

Example 4A: Multiplying Polynomials

(x – 5)(x2 + 4x – 6)

(x – 5 )(x2 + 4x – 6)

x(x2 + 4x – 6) – 5(x2 + 4x – 6)

x(x2) + x(4x) + x(–6) – 5(x2) – 5(4x) – 5(–6)

x3 + 4x2 – 5x2 – 6x – 20x + 30

x3 – x2 – 26x + 30

Distribute x.

Distribute x again.

Simplify.

Combine like terms.



Multiply.

Example 4B: Multiplying Polynomials

(2x – 5)(–4x2 – 10x + 3)

(2x – 5)(–4x2 – 10x + 3)

–4x2 – 10x + 32x – 5x

20x2 + 50x – 15+ –8x3 – 20x2 + 6x

–8x3 + 56x – 15

Multiply each term in the

top polynomial by –5.


top polynomial by 2x,

and align like terms.

Combine like terms by

adding vertically.



Multiply.

Example 4C: Multiplying Polynomials

(x + 3)3

[x · x + x(3) + 3(x) + (3)(3)]

[x(x+3) + 3(x+3)](x + 3)

(x2 + 3x + 3x + 9)(x + 3)

(x2 + 6x + 9)(x + 3)

Write as the product of

three binomials.

Use the FOIL method on

the first two factors.

Multiply.

Combine like terms.



Example 4C: Multiplying Polynomials Continued

Multiply.

(x + 3)3

x3 + 6x2 + 9x + 3x2 + 18x + 27

x3 + 9x2 + 27x + 27

x(x2) + x(6x) + x(9) + 3(x2) + 3(6x) + 3(9)

x(x2 + 6x + 9) + 3(x2 + 6x + 9)

Use the Commutative

Property of

Multiplication.

Distribute.

Distribute again.

(x + 3)(x2 + 6x + 9)

Combine like terms.



Example 4D: Multiplying Polynomials

Multiply.

(3x + 1)(x3 + 4x2 – 7)

x3 –4x2 –7

3x4 –12x3 –21x

–4x2x3 –7

3x

+1

3x4 – 12x3 + x3 – 4x2 – 21x – 7

Write the product of the

monomials in each

row and column.

Add all terms inside the

rectangle.

3x4 – 11x3 – 4x2 – 21x – 7 Combine like terms.



A polynomial with m terms multiplied by a polynomial with n terms has a product that, before simplifying has mn terms. In Example 4A, there are 2 3, or 6 terms before simplifying.

Helpful Hint

••••



Check It Out! Example 4a

Multiply.

(x + 3)(x2 – 4x + 6)

(x + 3 )(x2 – 4x + 6)

x(x2 – 4x + 6) + 3(x2 – 4x + 6)

Distribute.

Distribute again.

x(x2) + x(–4x) + x(6) +3(x2) +3(–4x) +3(6)

x3 – 4x2 + 3x2 +6x – 12x + 18

x3 – x2 – 6x + 18

Simplify.

Combine like terms.



Check It Out! Example 4b

Multiply.

(3x + 2)(x2 – 2x + 5)

(3x + 2)(x2 – 2x + 5)

x2 – 2x + 53x + 2×


top polynomial by 2.


top polynomial by 3x,

and align like terms.2x2 – 4x + 10+ 3x3 – 6x2 + 15x

3x3 – 4x2 + 11x + 10Combine like terms by

adding vertically.



Example 5: ApplicationThe width of a rectangular prism is 3 feet less than the height, and the length of the prism is 4 feet more than the height.

a. Write a polynomial that represents the area of the

base of the prism.

Write the formula for the

area of a rectangle.

Substitute h – 3 for w

and h + 4 for l.

A = l •••• w

A = l w•

A = (h + 4)(h – 3)

Multiply.A = h2 + 4h – 3h – 12

Combine like terms.A = h2 + h – 12

The area is represented by h2 + h – 12.



Example 5: Application ContinuedThe width of a rectangular prism is 3 feet less than the height, and the length of the prism is 4 feet more than the height.

b. Find the area of the base when the height is 5 ft.

A = h2 + h – 12

A = h2 + h – 12

A = 52 + 5 – 12

A = 25 + 5 – 12

A = 18

Write the formula for the area

the base of the prism.

Substitute 5 for h.

Simplify.

Combine terms.

The area is 18 square feet.




The length of a rectangle is 4 meters shorter than its width.

a. Write a polynomial that represents the area of the

rectangle.

Write the formula for the

area of a rectangle.

Substitute x – 4 for l and

x for w.

A = l w••••

A = l w•

A = x(x – 4)

Multiply.A = x2 – 4x

The area is represented by x2 – 4x.



Check It Out! Example 5 Continued

The length of a rectangle is 4 meters shorter than its width.

b. Find the area of a rectangle when the width is 6

meters.

A = x2 – 4x

A = x2 – 4x

A = 36 – 24

A = 12

Write the formula for the area of a

rectangle whose length is 4

meters shorter than width . Substitute 6 for x.

Simplify.

Combine terms.

The area is 12 square meters.

A = 62 – 4 • 6



Lesson Quiz: Part I

Multiply.

1. (6s2t2)(3st)

2. 4xy2(x + y)

3. (x + 2)(x – 8)

4. (2x – 7)(x2 + 3x – 4)

5. 6mn(m2 + 10mn – 2)

6. (2x – 5y)(3x + y)

4x2y2 + 4xy3

18s3t3

x2 – 6x – 16

2x3 – x2 – 29x + 28

6m3n + 60m2n2 – 12mn

6x2 – 13xy – 5y2



Lesson Quiz: Part II

7. A triangle has a base that is 4cm longer than its height.

a. Write a polynomial that represents the area of the triangle.

b. Find the area when the height is 8 cm.

48 cm2

1

2h2 + 2h

Lesson 6-5 Multiplying Polynomials · 2018. 9. 4. · Holt McDougal Algebra 1 6-5 Multiplying Polynomials To multiply monomials and polynomials, you will use some of the properties

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