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Solve: ( 3 r + 4 ) 2 = −8 .

no real solution

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Solve: ( 2 t 8 ) 2 = −10 .

no real solution

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The left sides of the equations in the next two examples do not seem to be of the form a ( x h ) 2 . But they are perfect square trinomials, so we will factor to put them in the form we need.

Solve: p 2 10 p + 25 = 18 .

Solution

The left side of the equation is a perfect square trinomial. We will factor it first.

p 2 10 p + 25 = 18 Factor the perfect square trinomial. ( p 5 ) 2 = 18 Use the Square Root Property. p 5 = ± 18 Simplify the radical. p 5 = ± 3 2 Solve for p . p = 5 ± 3 2 Rewrite to show two solutions. p = 5 + 3 2 , p = 5 3 2 Check. We leave the check for you.

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Solve: x 2 6 x + 9 = 12 .

x = 3 + 2 3 , x = 3 2 3

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Solve: y 2 + 12 y + 36 = 32 .

y = −6 + 4 2 , y = −6 4 2

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Solve: 4 n 2 + 4 n + 1 = 16 .

Solution

Again, we notice the left side of the equation is a perfect square trinomial. We will factor it first.

4 n 2 + 4 n + 1 = 16
Factor the perfect square trinomial. ( 2 n + 1 ) 2 = 16
Use the Square Root Property. 2 n + 1 = ± 16
Simplify the radical. 2 n + 1 = ± 4
Solve for n . 2 n = 1 ± 4
Divide each side by 2. 2 n 2 = 1 ± 4 2 n = 1 ± 4 2
Rewrite to show two solutions. n = 1 + 4 2 , n = 1 4 2
Simplify each equation. n = 3 2 , n = 5 2
Check.
.
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Solve: 9 m 2 12 m + 4 = 25 .

m = 7 , m = −3

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Solve: 16 n 2 + 40 n + 25 = 4 .

n = 3 4 , n = 7 4

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Access these online resources for additional instruction and practice with solving quadratic equations:

Key concepts

  • Square Root Property
    If x 2 = k , and k 0 , then x = k or x = k .

Practice makes perfect

Solve Quadratic Equations of the form a x 2 = k Using the Square Root Property

In the following exercises, solve the following quadratic equations.

r 2 24 = 0

r = ± 2 6

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u 2 300 = 0

u = ± 10 3

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x 2 + 20 = 0

no real solution

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2 5 a 2 + 3 = 11

a = ± 2 5

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7 p 2 + 10 = 26

p = ± 4 7 7

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Solve Quadratic Equations of the Form a ( x h ) 2 = k Using the Square Root Property

In the following exercises, solve the following quadratic equations.

( x + 2 ) 2 = 9

x = 1 , x = −5

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( u 6 ) 2 = 64

u = 14 , u = −2

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( m 6 ) 2 = 20

m = 6 ± 2 5

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( r 1 2 ) 2 = 3 4

r = 1 2 ± 3 2

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( a 7 ) 2 + 5 = 55

a = 7 ± 5 2

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( b 1 ) 2 9 = 39

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( 5 c + 1 ) 2 = −27

no real solution

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m 2 4 m + 4 = 8

m = 2 ± 2 2

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25 x 2 30 x + 9 = 36

x = 3 5 , x = 9 5

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Mixed Practice

In the following exercises, solve using the Square Root Property.

( a 4 ) 2 = 28

a = 4 ± 2 7

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9 w 2 24 w + 16 = 1

w = 1 , w = 5 3

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a 2 18 = 0

a = ± 3 2

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( p 1 3 ) 2 = 7 9

p = 1 3 ± 7 3

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m 2 + 12 = 0

no real solution

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u 2 14 u + 49 = 72

u = 7 ± 6 2

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( m 4 ) 2 + 3 = 15

m = 4 ± 2 3

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( n 7 ) 2 8 = 64

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( x + 5 ) 2 = 4

x = −3 , x = −7

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6 c 2 + 4 = 29

c = ± 5 6 6

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( x 6 ) 2 + 7 = 3

no real solution

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Everyday math

Paola has enough mulch to cover 48 square feet. She wants to use it to make three square vegetable gardens of equal sizes. Solve the equation 3 s 2 = 48 to find s , the length of each garden side.

4 feet

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Kathy is drawing up the blueprints for a house she is designing. She wants to have four square windows of equal size in the living room, with a total area of 64 square feet. Solve the equation 4 s 2 = 64 to find s , the length of the sides of the windows.

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Writing exercises

Explain why the equation x 2 + 12 = 8 has no solution.

Answers will vary.

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Explain why the equation y 2 + 8 = 12 has two solutions.

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Self check

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

This table has three rows and four columns. The first row is a header row and it labels each column. The first column is labeled “I can …”, the second “Confidently”, the third “With some help” and the last “No–I don’t get it”. In the “I can…” column the next row reads “solve quadratic equations of the form a x squared equals k using the square root property.” and the last row reads “solve quadratic equations of the form a times the quantity x minus h squared equals k using the square root property.” The remaining columns are blank.

If most of your checks were:

…confidently: Congratulations! You have achieved the objectives in this section. Reflect on the study skills you used so that you can continue to use them. What did you do to become confident of your ability to do these things? Be specific.

…with some help: This must be addressed quickly because topics you do not master become potholes in your road to success. In math, every topic builds upon previous work. It is important to make sure you have a strong foundation before you move on. Who can you ask for help? Your fellow classmates and instructor are good resources. Is there a place on campus where math tutors are available? Can your study skills be improved?

…no-I don’t get it! This is a warning sign and you must not ignore it. You should get help right away or you will quickly be overwhelmed. See your instructor as soon as you can to discuss your situation. Together you can come up with a plan to get you the help you need.

Practice Key Terms 2

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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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