x^2 + 8x = 20
x^2 + 8x - 20 = 0
Completing the square method:
(x^2 + 8x) - 20 = 0
(x + 4)^2 -16 - 20 = 0
(x + 4)^2 - 36 = 0
(x + 4)^2 = 36
x + 4 = sqrt(36) or = -sqrt(36)
x + 4 = 6 or = -6
x = 6 - 4 or x = -6 - 4
x = 2 or x = -10
Quadratic formula method:
x^2 + 8x - 20 = 0
(1)x^2 + (8)x + (-20) = 0
x = [-8 +/- sqrt(8^2 - 4(1)(-20))] / [2(1)]
x = [-8 +/- sqrt(144)] / 2
x = [-8 +/- 12] / 2
x = [-8 + 12] / 2 or x = [-8 - 12] / 2
x = 4 / 2 or x = -20 / 2
x = 2 or x = -10