Chapter 5 - Polynomials and Factoring - 5.2 Factoring Trinomials of the Type x2+bx+c - 5.2 Exercise Set - Page 317: 23

$(x+5)(x-3)$

The 2 numbers whose product is $ac= 1(-15)=-15 $ and whose sum is $b= 2 $ are $\left\{ 5,-3 \right\}.$ Using these two numbers to decompose the middle term of the given trinomial, $ x^2+2x-15 ,$ then the factored form is \begin{array}{l} x^2+5x-3x-15 \\\\= (x^2+5x)-(3x+15) \\\\= x(x+5)-3(x+5) \\\\= (x+5)(x-3) .\end{array}