Chapter 5 - Exponents and Polynomials - 5.3 - Multiplying Polynomials - Problem Set 5.3 - Page 207: 16

$x^2-2x-80$

Using the Distributive Property and then combining similar terms, the given expression, $ (x-10)(x+8) ,$ is equivalent to \begin{array}{l}\require{cancel} x(x)+x(8)-10(x)-10(8) \\\\= x^2+8x-10x-80 \\\\= x^2-2x-80 .\end{array}