Question

Solve the equation

x^2 + 4x - 7
By completing the square
give answer correct to two decimal places.
( p.s the answer is not -5.32 or 1.32 )

Answer 1

x = 1.32, -5.32

Explanation:

x^2 + 4x - 7

Set equal to zero

x^2 + 4x - 7 =0

Add 7 to each side

x^2 + 4x =7

Take the coefficient of x and divide by 2

4/2

Square it

2^2 =4

Add to each side

x^2+4x+4 = 7+4

(x+2)^2 = 11

Take the square root of each side

x+2 = ±sqrt(11)

Subtract 2 from each side

x = -2 ±sqrt(11)

x=1.31662

x=-5.31662

To 2 decimal places

x = 1.32, -5.32