Chapter 5 - Polynomials and Polynomial Functions - 5-1 Polynomial Functions - Practice and Problem-Solving Exercises - Page 287: 70

$x^2+8x-20=(x+10)(x-2)$

The leading coefficient is 1. Thus, to factor the trinomial, just look for factors of $-20$ whose sum is equal to the coefficient of the middle term. Note that $-20=10(-2) \text{ and } 10+(-2)=8$. Therefore, the factored form of the trinomial is $(x+10)(x-2)$.