A b and c are taken from the quadratic equation written in its general form of. So its fast and easy when its usable but not always factorable either. One of the numbers has to be negative to make 36 so by playing with a few different numbers I find that 4 and 9 work nicely.
You should memorize the quadratic formula if you havent done so already.
A product of factors is zero if and only if one or more of the factors is zero. If we replace 0 with y then we get a quadratic function. Ax 2 bx c 0. Square this number and add to both sides of the equation.