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Multiply a trinomial by a binomial

We have multiplied monomials by monomials, monomials by polynomials, and binomials by binomials. Now we’re ready to multiply a trinomial    by a binomial    . Remember, FOIL will not work in this case, but we can use either the Distributive Property or the Vertical Method. We first look at an example using the Distributive Property.

Multiply using the Distributive Property: ( b + 3 ) ( 2 b 2 5 b + 8 ) .

Solution

The product of a binomial, b plus 3, and a trinomial, 2 b squared minus 5 b plus 8. Two arrows extend from the trinomial, terminating at b and 3 in the binomial.
Distribute. The sum of two products, the product of b and 2 b squared minus 5 b plus 8, and the product of 3 and 2 b squared minus 5 b plus 8.
Multiply. 2 b cubed minus 5 b squared plus 8 b plus 6 b squared minus 15 b plus 24.
Combine like terms. 2 b cubed plus b squared minus 7 b plus 24.

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Multiply using the Distributive Property: ( y 3 ) ( y 2 5 y + 2 ) .

y 3 8 y 2 + 17 y 6

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Multiply using the Distributive Property: ( x + 4 ) ( 2 x 2 3 x + 5 ) .

2 x 3 + 5 x 2 7 x + 20

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Now let’s do this same multiplication using the Vertical Method.

Multiply using the Vertical Method: ( b + 3 ) ( 2 b 2 5 b + 8 ) .

Solution

It is easier to put the polynomial with fewer terms on the bottom because we get fewer partial products this way.

Multiply (2 b 2 − 5 b + 8) by 3. .
.
Multiply (2 b 2 − 5 b + 8) by b. .
Add like terms.

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Multiply using the Vertical Method: ( y 3 ) ( y 2 5 y + 2 ) .

y 3 8 y 2 + 17 y 6

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Multiply using the Vertical Method: ( x + 4 ) ( 2 x 2 3 x + 5 ) .

2 x 3 + 5 x 2 7 x + 20

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We have now seen two methods you can use to multiply a trinomial    by a binomial. After you practice each method, you’ll probably find you prefer one way over the other. We list both methods are listed here, for easy reference.

Multiplying a trinomial by a binomial

To multiply a trinomial by a binomial, use the:

  • Distributive Property
  • Vertical Method

Access these online resources for additional instruction and practice with multiplying polynomials:

Key concepts

  • FOIL Method for Multiplying Two Binomials —To multiply two binomials:
    1. Multiply the First terms.
    2. Multiply the Outer terms.
    3. Multiply the Inner terms.
    4. Multiply the Last terms.

  • Multiplying Two Binomials —To multiply binomials, use the:
  • Multiplying a Trinomial by a Binomial —To multiply a trinomial by a binomial, use the:
    • Distributive Property ( [link] )
    • Vertical Method ( [link] )

Practice makes perfect

Multiply a Polynomial by a Monomial

In the following exercises, multiply.

−3 ( a + 7 )

−3 a 21

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2 ( x 7 )

2 x 14

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−3 ( k 4 )

−3 k + 12

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b ( b + 9 )

b 2 9 b

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x ( x 10 )

x 2 + 10 x

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6 r ( 4 r + s )

24 r 2 + 6 r s

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12 x ( x 10 )

12 x 2 120 x

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−9 a ( 3 a + 5 )

−27 a 2 45 a

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3 ( p 2 + 10 p + 25 )

3 p 2 + 30 p + 75

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−8 x ( x 2 + 2 x 15 )

−8 x 3 16 x 2 + 120 x

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−5 t ( t 2 + 3 t 18 )

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5 q 3 ( q 3 2 q + 6 )

5 q 6 10 q 4 + 30 q 3

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4 x 3 ( x 4 3 x + 7 )

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−8 y ( y 2 + 2 y 15 )

−8 y 3 16 y 2 + 120 y

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−5 m ( m 2 + 3 m 18 )

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5 q 3 ( q 2 2 q + 6 )

5 q 5 10 q 4 + 30 q 3

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9 r 3 ( r 2 3 r + 5 )

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−4 z 2 ( 3 z 2 + 12 z 1 )

−12 z 4 48 z 3 + 4 z 2

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−3 x 2 ( 7 x 2 + 10 x 1 )

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( 2 m 9 ) m

2 m 2 9 m

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( w 6 ) · 8

8 w 48

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15 ( r 24 )

15 r 360

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−3 ( m + 11 )

−3 m 33

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−8 ( z 5 )

−8 z + 40

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n ( n 2 3 n )

n 3 3 n 2

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6 x ( 4 x + y )

24 x 2 + 6 x y

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5 p ( 11 p 5 q )

55 p 2 25 p q

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3 ( v 2 + 10 v + 25 )

3 v 2 + 30 v + 75

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2 n ( 4 n 2 4 n + 1 )

8 n 3 8 n 2 + 2 n

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3 r ( 2 r 2 6 r + 2 )

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−8 y ( y 2 + 2 y 15 )

−8 y 3 16 y 2 + 120 y

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−5 m ( m 2 + 3 m 18 )

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5 q 3 ( q 2 2 q + 6 )

5 q 5 10 q 4 + 30 q 3

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9 r 3 ( r 2 3 r + 5 )

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−4 z 2 ( 3 z 2 + 12 z 1 )

−12 z 4 48 z 3 + 4 z 2

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−3 x 2 ( 7 x 2 + 10 x 1 )

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( 2 y 9 ) y

18 y 2 9 y

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Multiply a Binomial by a Binomial

In the following exercises, multiply the following binomials using: the Distributive Property the FOIL method the Vertical Method.

( w + 5 ) ( w + 7 )

w 2 + 12 w + 35

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( p + 11 ) ( p 4 )

p 2 + 7 p 44

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In the following exercises, multiply the binomials. Use any method.

( x + 8 ) ( x + 3 )

x 2 + 11 x + 24

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( y 6 ) ( y 2 )

y 2 8 y + 12

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( w 4 ) ( w + 7 )

w 2 + 3 w 28

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( p + 12 ) ( p 5 )

p 2 + 7 p 60

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( 6 p + 5 ) ( p + 1 )

6 p 2 + 11 p + 5

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( 2 t 9 ) ( 10 t + 1 )

20 t 2 88 t 9

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( 3 r 8 ) ( 11 r + 1 )

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( 5 x y ) ( 3 x 6 )

15 x 2 3 x y 30 x + 6 y

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( 10 a b ) ( 3 a 4 )

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( a + b ) ( 2 a + 3 b )

2 a 2 + 5 a b + 3 b 2

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( 4 z y ) ( z 6 )

4 z 2 24 z z y + 6 y

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( 5 x y ) ( x 4 )

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( x 2 + 3 ) ( x + 2 )

x 3 + 2 x 2 + 3 x + 6

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( x 2 + 8 ) ( x 2 5 )

x 4 + 3 x 2 40

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( y 2 7 ) ( y 2 4 )

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( 5 a b 1 ) ( 2 a b + 3 )

10 a 2 b 2 + 13 a b 3

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( 2 x y + 3 ) ( 3 x y + 2 )

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( 6 p q 3 ) ( 4 p q 5 )

24 p 2 q 2 42 p q + 15

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( 3 r s 7 ) ( 3 r s 4 )

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Multiply a Trinomial by a Binomial

In the following exercises, multiply using the Distributive Property the Vertical Method.

( x + 5 ) ( x 2 + 4 x + 3 )

x 3 + 9 x 2 + 23 x + 15

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( u + 4 ) ( u 2 + 3 u + 2 )

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( y + 8 ) ( 4 y 2 + y 7 )

4 y 3 + 33 y 2 + y 56

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( a + 10 ) ( 3 a 2 + a 5 )

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In the following exercises, multiply. Use either method.

( w 7 ) ( w 2 9 w + 10 )

w 3 16 w 2 + 73 w 70

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( p 4 ) ( p 2 6 p + 9 )

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( 3 q + 1 ) ( q 2 4 q 5 )

3 q 3 11 q 2 19 q 5

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( 6 r + 1 ) ( r 2 7 r 9 )

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Mixed Practice

( 10 y 6 ) + ( 4 y 7 )

14 y 13

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( 15 p 4 ) + ( 3 p 5 )

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( x 2 4 x 34 ) ( x 2 + 7 x 6 )

−11 x 28

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( j 2 8 j 27 ) ( j 2 + 2 j 12 )

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5 q ( 3 q 2 6 q + 11 )

15 q 3 30 q 2 + 55 q

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8 t ( 2 t 2 5 t + 6 )

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( s 7 ) ( s + 9 )

s 2 + 2 s 63

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( y 2 2 y ) ( y + 1 )

y 3 y 2 2 y

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( a 2 3 a ) ( 4 a + 5 )

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( 3 n 4 ) ( n 2 + n 7 )

3 n 3 n 2 25 n + 28

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( 6 k 1 ) ( k 2 + 2 k 4 )

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( 7 p + 10 ) ( 7 p 10 )

49 p 2 100

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( 3 y + 8 ) ( 3 y 8 )

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( 4 m 2 3 m 7 ) m 2

4 m 4 3 m 3 7 m 2

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( 15 c 2 4 c + 5 ) c 4

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( 5 a + 7 b ) ( 5 a + 7 b )

25 a 2 + 70 a b + 49 b 2

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( 3 x 11 y ) ( 3 x 11 y )

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( 4 y + 12 z ) ( 4 y 12 z )

16 y 2 144 z 2

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Everyday math

Mental math You can use binomial multiplication to multiply numbers without a calculator. Say you need to multiply 13 times 15. Think of 13 as 10 + 3 and 15 as 10 + 5 .

  1. Multiply ( 10 + 3 ) ( 10 + 5 ) by the FOIL method.
  2. Multiply 13 · 15 without using a calculator.
  3. Which way is easier for you? Why?
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Mental math You can use binomial multiplication to multiply numbers without a calculator. Say you need to multiply 18 times 17. Think of 18 as 20 2 and 17 as 20 3 .

  1. Multiply ( 20 2 ) ( 20 3 ) by the FOIL method.
  2. Multiply 18 · 17 without using a calculator.
  3. Which way is easier for you? Why?

306 306 Answers will vary.

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Writing exercises

Which method do you prefer to use when multiplying two binomials: the Distributive Property, the FOIL method, or the Vertical Method? Why?

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Which method do you prefer to use when multiplying a trinomial by a binomial: the Distributive Property or the Vertical Method? Why?

Answers will vary.

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Multiply the following:

( x + 2 ) ( x 2 ) ( y + 7 ) ( y 7 ) ( w + 5 ) ( w 5 )

Explain the pattern that you see in your answers.

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Multiply the following:

( m 3 ) ( m + 3 ) ( n 10 ) ( n + 10 ) ( p 8 ) ( p + 8 )

Explain the pattern that you see in your answers.

Answers may vary.

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Multiply the following:

( p + 3 ) ( p + 3 ) ( q + 6 ) ( q + 6 ) ( r + 1 ) ( r + 1 )

Explain the pattern that you see in your answers.

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Multiply the following:

( x 4 ) ( x 4 ) ( y 1 ) ( y 1 ) ( z 7 ) ( z 7 )

Explain the pattern that you see in your answers.

Answers may vary.

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Self check

After completing the exercises, use this checklist to evaluate your mastery of the objectives of this section.

This is a table that has four rows and four columns. In the first row, which is a header row, the cells read from left to right “I can…,” “Confidently,” “With some help,” and “No-I don’t get it!” The first column below “I can…” reads “multiply a polynomial by a monomial,” “multiply a binomial by a binomial,” and “multiply a trinomial by a binomial.” The rest of the cells are blank.

What does this checklist tell you about your mastery of this section? What steps will you take to improve?

Questions & Answers

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Source:  OpenStax, Elementary algebra. OpenStax CNX. Jan 18, 2017 Download for free at http://cnx.org/content/col12116/1.2
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