2-5 Quizizz Complete Square Practice

Find the value that completes the square and then rewrite as a perfect square.

a² - 40a + ____

• 1600; (a - 20)²

• -20; (a - 20)²

• 81; (a - 9)²

• 400; (a - 20)²

Answer explanation

Divide -40 by 2. Square it for the first answer. Second answer is (a plus first result).

Find the value that completes the square.
x2 + 4x + ___

Answer explanation

Divide +4 by 2.

Rewrite as a perfect square.
 $x^2+4x+_{ }$  ____

Answer explanation

Answer is (x plus result)^2.

Solve the equation by completing the square.

• A

• B

• C

• D

Answer explanation

Subtract 20 from both sides.

Do +6/2. Then square it.

Add that to both sides.

Rewrite the left side as (x + (+6/2))^2

Take the square root of both sides.

Remember to use +- square root on right side.

Now, solve for x.

You should have two answers.

Solve. You might want to complete the square.

 $x^2-4x-11=10$  
Write just the answers without "x".

Answer explanation

Add 11 to both sides.
Do -4/2. Then square it.
Add that to both sides.
Rewrite the left side as (x + (-4/2))^2
Take the square root of both sides.
Remember to use +- square root on right side.
Now, solve for x.
You should have two answers.

Solve. You might want to complete the square.

 $x^2+14=15$  
Write just the answers without "x".

Answer explanation

Do 14/2. Then square it.
Add that to both sides.
Rewrite the left side as (x + (14/2))^2
Take the square root of both sides.
Remember to use +- square root on right side.
Now, solve for x.
You should have two answers.

Solve. You might want to complete the square.

 $x^2=-21+8x$  
Write just the answers without "x".

Answer explanation

Subtract 8x from both sides.

Do -8/2. Then square it.

Add that to both sides.
Rewrite the left side as (x + __)^2
Take the square root of both sides.
Remember to use +- square root on right side.
Now, solve for x.
You should have two answers.

Did you take the square root of a negative number?

Solve. You might want to complete the square.

 $x^2-16x=20$  
Write just the answers without "x".

Answer explanation

Do b/2. Then square it.

Add that to both sides.
Rewrite the left side as (x + __)^2
Take the square root of both sides.
Remember to use +- square root on right side.
Now, solve for x.
You should have two answers.

Did you take the square root of a negative number?

Solve. You might want to complete the square.

 $x^2+21x+45=3x$  
Write just the answers without "x".

Answer explanation

Subtract 45 from both sides.

Subtract 3x from both sides.

Do b/2. Then square it.

Add that to both sides.
Rewrite the left side as (x + __)^2
Take the square root of both sides.
Remember to use +- square root on right side.
Now, solve for x.
You should have two answers.

Did you take the square root of a negative number?

Solve. You might want to complete the square.

 $x^2+10x+3=6x$  
Write just the answers without "x".

Answer explanation

Subtract 3 from both sides.

Subtract 6x from both sides.

Do b/2. Then square it.

Add that to both sides.
Rewrite the left side as (x + __)^2
Take the square root of both sides.
Remember to use +- square root on right side.
Now, solve for x.
You should have two answers.

Did you take the square root of a negative number?