x^2 - 10x + 8 = 0 subtract 8 from both sides
x^2 - 10x = - 8 take 1/2 of 10 = 5....square it = 25 add to both sides
x^2 - 10x + 25 = - 8 + 25 factor the left and simplify
( x - 5)^2 = 17 take both roots
x - 5 = ±√17 add 5 to both sides
x = ±√(17) + 5
-8 was the isolated constant
2x^2 + 8x - 12 = 0 divide through by 2
x^2 + 4x - 6 = 0 add 6 to both sides
x^2 + 4x = 6 take 1/2 of 4 = 2.....square this = 4........add to both sides
x^2 + x + 4 = 6 + 4 factor the left and simplify
(x + 2)^2 = 10 take both roots
x + 2 = ±√10 subtract 2 from both sides
x = ±√(10) - 2