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Key concepts

  • Zero Product Property If a · b = 0 , then either a = 0 or b = 0 or both. See [link] .
  • Solve a quadratic equation by factoring To solve a quadratic equation by factoring: See [link] .
    1. Write the quadratic equation in standard form, a x 2 + b x + c = 0 .
    2. Factor the quadratic expression.
    3. Use the Zero Product Property.
    4. Solve the linear equations.
    5. Check.
  • Use a problem solving strategy to solve word problems See [link] .
    1. Read the problem. Make sure all the words and ideas are understood.
    2. Identify what we are looking for.
    3. Name what we are looking for. Choose a variable to represent that quantity.
    4. Translate into an equation. It may be helpful to restate the problem in one sentence with all the important information. Then, translate the English sentence into an algebra equation.
    5. Solve the equation using good algebra techniques.
    6. Check the answer in the problem and make sure it makes sense.
    7. Answer the question with a complete sentence.

Practice makes perfect

Use the Zero Product Property

In the following exercises, solve.

( x 3 ) ( x + 7 ) = 0

x = 3 , x = −7

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( y 11 ) ( y + 1 ) = 0

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( 3 a 10 ) ( 2 a 7 ) = 0

a = 10 / 3 , a = 7 / 2

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( 5 b + 1 ) ( 6 b + 1 ) = 0

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6 m ( 12 m 5 ) = 0

m = 0 , m = 5 / 12

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( 2 x 1 ) 2 = 0

x = 1 / 2

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Solve Quadratic Equations by Factoring

In the following exercises, solve.

x 2 + 7 x + 12 = 0

x = 3 , x = 4 x = −3 , x = −4

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5 a 2 26 a = 24

a = −5 / 4 , a = 6 a = −4 / 5 , a = 6

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4 m 2 = 17 m 15

m = 5 / 4 , m = 3

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n 2 = 5 6 n n 2 = 5 n 6

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7 a 2 + 14 a = 7 a

a = −1 , a = 0

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12 b 2 15 b = −9 b

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49 m 2 = 144

m = 12 / 7 , m = −12 / 7

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( y 3 ) ( y + 2 ) = 4 y

y = −1 , y = 6

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( p 5 ) ( p + 3 ) = −7

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( 2 x + 1 ) ( x 3 ) = −4 x

x = 3 / 2 , x = −1

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( x + 6 ) ( x 3 ) = −8

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16 p 3 = 24 p 2 + 9 p

p = 0 , p = ¾

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20 x 2 60 x = −45

x = −2 / 3 x = 3 / 2

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Solve Applications Modeled by Quadratic Equations

In the following exercises, solve.

The product of two consecutive integers is 56. Find the integers.

7 and 8 ; 8 and −7

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The product of two consecutive integers is 42. Find the integers.

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The area of a rectangular carpet is 28 square feet. The length is three feet more than the width. Find the length and the width of the carpet.

4 feet and 7 feet

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A rectangular retaining wall has area 15 square feet. The height of the wall is two feet less than its length. Find the height and the length of the wall.

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A pennant is shaped like a right triangle, with hypotenuse 10 feet. The length of one side of the pennant is two feet longer than the length of the other side. Find the length of the two sides of the pennant.

6 feet and 8 feet

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A reflecting pool is shaped like a right triangle, with one leg along the wall of a building. The hypotenuse is 9 feet longer than the side along the building. The third side is 7 feet longer than the side along the building. Find the lengths of all three sides of the reflecting pool.

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Mixed Practice

In the following exercises, solve.

( x + 8 ) ( x 3 ) = 0

x = −8 , x = 3

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( 3 y 5 ) ( y + 7 ) = 0

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p 2 + 12 p + 11 = 0

p = −1 , p = −11

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m 2 = 6 m + 16

m = −2 , m = 8

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a 3 a 2 42 a = 0

a = 0 , a = −6 , a = 7

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4 b 2 60 b + 224 = 0

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The product of two consecutive integers is 110. Find the integers.

10 and 11 ; 11 and −10

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The length of one leg of a right triangle is three more than the other leg. If the hypotenuse is 15, find the lengths of the two legs.

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Everyday math

Area of a patio If each side of a square patio is increased by 4 feet, the area of the patio would be 196 square feet. Solve the equation ( s + 4 ) 2 = 196 for s to find the length of a side of the patio.

10 feet

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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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