The first term will be an x because
x squared breaks down as x times x.
First look for factors of your constant that add to your
coefficient of the middle term in the trinomial.
Also note that the constant is negative and a negative
factors as the product of a positive and a negative.
The factors of -20 that add to -8 are -10 and +2.
So we have y = (x - 10)(x + 2).
