Question

Solve by completing the square. x^2 + 4x – 1= 0

Answer 1

x = -2 ± sqrt(5)

Explanation:

x^2 + 4x – 1= 0

Add 1 to each side

x^2 + 4x – 1+1= 0+1

x^2 +4x = 1

Take the coefficient of x

4

Divide by 2

4/2 =2

Square it

2^2=4

Add it to each side

x^2 +4x+4=1+4

(x+2)^2 = 5

Take the square root of each side

sqrt((x+2)^2 )=± sqrt(5)

x+2 = ± sqrt(5)

Subtract 2 from each side

x+2-2 = -2 ± sqrt(5)

x = -2 ± sqrt(5)