Solve the quadratic equation: x^2 - 2x - 15 = 0

We need to find numbers that multiply together to give -15. This could be -1 and 15, 1 and -15, -3 and 5, 3 and -5. The numbers we need must add up to -2 as well (from -2x term). Therefore our set must be 3 and -5.

So we get (x+3)(x-5)=0 with x=-3 and x=5