a² -2a -8 = 0 Move the non-x term to the right a² -2a = 8 Divide equation by coefficient of a^2 (not necessary). Take the coefficient of x (which is -2) divide it by 2 square it add it to both sides of the equation -2 / 2 = -1 -1 ^2 = 1
a² -2a +1= 8 +1
(a -1) * (a-1) = 9
Take the square root of both sides
(a-1) = 3 a = 4
Remember that square root of 9 ALSO = -3 (a-1) = -3 a = -2
