equation : x^2 - 9x - 12 = 4x - 6. add six to both sides and add 4x to both sides to get x^2 - 5x - 6 = 0. find two numbers that add to -5 and multiply to -6, which would be -6 and 1. substitute in with x to get x^2 - 6x + 1x - 6 = 0. take out the x and the 1 to get x(x-6)+1(x-6) = 0. so x = -1 and x = 6.
