Question

4.

Solve the equation by completing the square. Round to the nearest hundredth if necessary. 4x2 + 8x – 32 = 0

A. 2.65, 3
B. 2, –4
C. 2, –10
D. –52, 44

Answer 1

B

Explanation:

Given

4x² + 8x - 32 = 0 ( divide through by 4 )

x² + 2x - 8 = 0 ( add 8 to both sides )

x² + 2x = 8

To complete the square

add ( half the coefficient of the x- term)² to both sides

x² + 2(1)x + 1 = 8 + 1

(x + 1)² = 9 ( take the square root of both sides )

x + 1 = ±
`√(9)` = ± 3 ( subtract 1 from both sides )

x = - 1 ± 3

Then

x = - 1 + 3 = 2

x = - 1 - 3 = - 4

Answer 2

x = 2, -4

Explanation:

4x^2 + 8x – 32 = 0

Divide by 4

x^2 + 2x – 8 = 0

Add 8 to each side

x^2 + 2x = 8

Take the coefficient of x

2

Divide by 2

2/2 =1

Square it

1^2=1

Add it to each side

x^2+2x+1 = 8+1

(x+1)^2 = 9

Take the square root of each side

sqrt((x+1)^2) = ±sqrt(9)

x+1 = ±3

Subtract 1 from each side

x = -1±3

x = -1+3, -1-3

x = 2, -4