<< Chapter < Page Chapter >> Page >

Sometimes the coefficient can be factored from all three terms of the trinomial. This will be our strategy in the next example.

Solve 3 x 2 12 x 15 = 0 by completing the square.

Solution

To complete the square, we need the coefficient of x 2 to be one. If we factor out the coefficient of x 2 as a common factor, we can continue with solving the equation by completing the square.

.
Factor out the greatest common factor. .
Divide both sides by 3 to isolate the trinomial. .
Simplify. .
Subtract 5 to get the constant terms on the right. .
Take half of 4 and square it. ( 1 2 ( 4 ) ) 2 = 4 .
Add 4 to both sides. .
Factor the perfect square trinomial as a binomial square. .
Use the Square Root Property. .
Solve for x. .
Rewrite to show 2 solutions. .
Simplify. .
Check.
.

Got questions? Get instant answers now!
Got questions? Get instant answers now!

Solve 2 m 2 + 16 m 8 = 0 by completing the square.

m = −4 ± 2 5

Got questions? Get instant answers now!

Solve 4 n 2 24 n 56 = 8 by completing the square.

n = −2 , 8

Got questions? Get instant answers now!

To complete the square, the leading coefficient must be one. When the leading coefficient is not a factor of all the terms, we will divide both sides of the equation by the leading coefficient. This will give us a fraction for the second coefficient. We have already seen how to complete the square with fractions in this section.

Solve 2 x 2 3 x = 20 by completing the square.

Solution

Again, our first step will be to make the coefficient of x 2 be one. By dividing both sides of the equation by the coefficient of x 2 , we can then continue with solving the equation by completing the square.

.
Divide both sides by 2 to get the coefficient of x 2 to be 1. .
Simplify. .
Take half of 3 2 and square it. ( 1 2 ( 3 2 ) ) 2 = 9 16 .
Add 9 16 to both sides. .
Factor the perfect square trinomial as a binomial square. .
Add the fractions on the right side. .
Use the Square Root Property. .
Simplify the radical. .
Solve for x. .
Rewrite to show 2 solutions. .
Simplify. .
Check. We leave the check for you.
Got questions? Get instant answers now!
Got questions? Get instant answers now!

Solve 3 r 2 2 r = 21 by completing the square.

r = 7 3 , r = 3

Got questions? Get instant answers now!

Solve 4 t 2 + 2 t = 20 by completing the square.

t = 5 2 , t = 2

Got questions? Get instant answers now!

Solve 3 x 2 + 2 x = 4 by completing the square.

Solution

Again, our first step will be to make the coefficient of x 2 be one. By dividing both sides of the equation by the coefficient of x 2 , we can then continue with solving the equation by completing the square.

.
Divide both sides by 3 to make the coefficient of x 2 equal 1. .
Simplify. .
Take half of 2 3 and square it. ( 1 2 2 3 ) 2 = 1 9 .
Add 1 9 to both sides. .
Factor the perfect square trinomial as a binomial square. .
Use the Square Root Property. .
Simplify the radical. .
Solve for x . .
Rewrite to show 2 solutions. .
Check. We leave the check for you.
Got questions? Get instant answers now!
Got questions? Get instant answers now!

Solve 4 x 2 + 3 x = 12 by completing the square.

x = 3 8 ± 201 8

Got questions? Get instant answers now!

Solve 5 y 2 + 3 y = 10 by completing the square.

y = 3 10 ± 209 10

Got questions? Get instant answers now!

Access these online resources for additional instruction and practice with solving quadratic equations by completing the square:

Key concepts

  • Binomial Squares Pattern If a , b are real numbers,
    ( a + b ) 2 = a 2 + 2 a b + b 2

    ( a b ) 2 = a 2 2 a b + b 2
  • Complete a Square
    To complete the square of x 2 + b x :
    1. Identify b , the coefficient of x .
    2. Find ( 1 2 b ) 2 , the number to complete the square.
    3. Add the ( 1 2 b ) 2 to x 2 + b x .

Practice makes perfect

Complete the Square of a Binomial Expression

In the following exercises, complete the square to make a perfect square trinomial. Then, write the result as a binomial squared.

m 2 24 m

( m 12 ) 2

Got questions? Get instant answers now!

p 2 22 p

( p 11 ) 2

Got questions? Get instant answers now!

x 2 9 x

( x 9 2 ) 2

Got questions? Get instant answers now!

p 2 1 3 p

( p 1 6 ) 2

Got questions? Get instant answers now!

Solve Quadratic Equations of the Form x 2 + b x + c = 0 by Completing the Square

In the following exercises, solve by completing the square.

v 2 + 6 v = 40

v = −10 , v = 4

Got questions? Get instant answers now!

u 2 + 2 u = 3

u = −3 , u = 1

Got questions? Get instant answers now!

c 2 12 c = 13

c = −1 , c = 13

Got questions? Get instant answers now!

x 2 20 x = 21

x = −1 , x = 21

Got questions? Get instant answers now!

m 2 + 4 m = −44

no real solution

Got questions? Get instant answers now!

r 2 + 6 r = −11

no real solution

Got questions? Get instant answers now!

a 2 10 a = −5

a = 5 ± 2 5

Got questions? Get instant answers now!

u 2 14 u + 12 = −1

u = 1 , u = 13

Got questions? Get instant answers now!

v 2 = 9 v + 2

v = 9 2 ± 89 2

Got questions? Get instant answers now!

( x + 6 ) ( x 2 ) = 9

x = −7 , x = 3

Got questions? Get instant answers now!

( y + 9 ) ( y + 7 ) = 79

Got questions? Get instant answers now!

Solve Quadratic Equations of the Form a x 2 + b x + c = 0 by Completing the Square

In the following exercises, solve by completing the square.

3 m 2 + 30 m 27 = 6

m = −11 , m = 1

Got questions? Get instant answers now!

2 c 2 + c = 6

c = −2 , c = 3 2

Got questions? Get instant answers now!

2 p 2 + 7 p = 14

p = 7 4 ± 161 4

Got questions? Get instant answers now!

Everyday math

Rafi is designing a rectangular playground to have an area of 320 square feet. He wants one side of the playground to be four feet longer than the other side. Solve the equation p 2 + 4 p = 320 for p , the length of one side of the playground. What is the length of the other side?

16 feet, 20 feet

Got questions? Get instant answers now!

Yvette wants to put a square swimming pool in the corner of her backyard. She will have a 3 foot deck on the south side of the pool and a 9 foot deck on the west side of the pool. She has a total area of 1080 square feet for the pool and two decks. Solve the equation ( s + 3 ) ( s + 9 ) = 1080 for s , the length of a side of the pool.

Got questions? Get instant answers now!

Writing exercises

Solve the equation x 2 + 10 x = −25 by using the Square Root Property and by completing the square. Which method do you prefer? Why?

−5 −5 Answers will vary.

Got questions? Get instant answers now!

Solve the equation y 2 + 8 y = 48 by completing the square and explain all your steps.

Got questions? Get instant answers now!

Self check

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

This table has four 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 “complete the square of a binomial expression.” The next row reads “solve quadratic equations of the form x squared plus b x plus c equals zero by completing the square.” and the last row reads “solve quadratic equations of the form a x squared plus b x plus c equals zero by completing the square.” The remaining columns are blank.

After reviewing this checklist, what will you do to become confident for all objectives?

Questions & Answers

what does preconceived mean
sammie Reply
physiological Psychology
Nwosu Reply
How can I develope my cognitive domain
Amanyire Reply
why is communication effective
Dakolo Reply
Communication is effective because it allows individuals to share ideas, thoughts, and information with others.
effective communication can lead to improved outcomes in various settings, including personal relationships, business environments, and educational settings. By communicating effectively, individuals can negotiate effectively, solve problems collaboratively, and work towards common goals.
it starts up serve and return practice/assessments.it helps find voice talking therapy also assessments through relaxed conversation.
miss
Every time someone flushes a toilet in the apartment building, the person begins to jumb back automatically after hearing the flush, before the water temperature changes. Identify the types of learning, if it is classical conditioning identify the NS, UCS, CS and CR. If it is operant conditioning, identify the type of consequence positive reinforcement, negative reinforcement or punishment
Wekolamo Reply
please i need answer
Wekolamo
because it helps many people around the world to understand how to interact with other people and understand them well, for example at work (job).
Manix Reply
Agreed 👍 There are many parts of our brains and behaviors, we really need to get to know. Blessings for everyone and happy Sunday!
ARC
A child is a member of community not society elucidate ?
JESSY Reply
Isn't practices worldwide, be it psychology, be it science. isn't much just a false belief of control over something the mind cannot truly comprehend?
Simon Reply
compare and contrast skinner's perspective on personality development on freud
namakula Reply
Skinner skipped the whole unconscious phenomenon and rather emphasized on classical conditioning
war
explain how nature and nurture affect the development and later the productivity of an individual.
Amesalu Reply
nature is an hereditary factor while nurture is an environmental factor which constitute an individual personality. so if an individual's parent has a deviant behavior and was also brought up in an deviant environment, observation of the behavior and the inborn trait we make the individual deviant.
Samuel
I am taking this course because I am hoping that I could somehow learn more about my chosen field of interest and due to the fact that being a PsyD really ignites my passion as an individual the more I hope to learn about developing and literally explore the complexity of my critical thinking skills
Zyryn Reply
good👍
Jonathan
and having a good philosophy of the world is like a sandwich and a peanut butter 👍
Jonathan
generally amnesi how long yrs memory loss
Kelu Reply
interpersonal relationships
Abdulfatai Reply
What would be the best educational aid(s) for gifted kids/savants?
Heidi Reply
treat them normal, if they want help then give them. that will make everyone happy
Saurabh
What are the treatment for autism?
Magret Reply
hello. autism is a umbrella term. autistic kids have different disorder overlapping. for example. a kid may show symptoms of ADHD and also learning disabilities. before treatment please make sure the kid doesn't have physical disabilities like hearing..vision..speech problem. sometimes these
Jharna
continue.. sometimes due to these physical problems..the diagnosis may be misdiagnosed. treatment for autism. well it depends on the severity. since autistic kids have problems in communicating and adopting to the environment.. it's best to expose the child in situations where the child
Jharna
child interact with other kids under doc supervision. play therapy. speech therapy. Engaging in different activities that activate most parts of the brain.. like drawing..painting. matching color board game. string and beads game. the more you interact with the child the more effective
Jharna
results you'll get.. please consult a therapist to know what suits best on your child. and last as a parent. I know sometimes it's overwhelming to guide a special kid. but trust the process and be strong and patient as a parent.
Jharna
Got questions? Join the online conversation and get instant answers!
Jobilize.com Reply
Practice Key Terms 1

Get Jobilize Job Search Mobile App in your pocket Now!

Get it on Google Play Download on the App Store Now




Source:  OpenStax, Elementary algebra. OpenStax CNX. Jan 18, 2017 Download for free at http://cnx.org/content/col12116/1.2
Google Play and the Google Play logo are trademarks of Google Inc.

Notification Switch

Would you like to follow the 'Elementary algebra' conversation and receive update notifications?

Ask