Chapter 5 - Section 5.2 - Multiplying Polynomials - Exercise Set - Page 359: 59

$x^2-2x-15$

Using $(a+b)(c+d)=ac+ad+bc+bd$ or the Distributive Property, the given expression, $ (x+3)(x-5) ,$ is equivalent to \begin{array}{l}\require{cancel} x(x)+x(-5)+3(x)+3(-5) \\\\= x^2-5x+3x-15 \\\\= x^2-2x-15 .\end{array}