Chapter 5 - Polynomials and Polynomial Functions - 5-2 Polynomials, Linear Factors, and Zeros - Practice and Problem-Solving Exercises - Page 295: 65

$x^2-2x-15=(x-5)(x+3)$

The leading coefficieint is 1. Thus, to factor the trinomial, look for the factors of the constant term (-15) whose sum is equal to the coefficient of the middle term (-2). Note that $-15=-5(3) \text{ and } -5+3=-2$. Thus, the factored form of the trinomial is $(x-5)(x+3)$.