Chapter 4 - Polynomials - 4.6 Special Products - 4.6 Exercise Set - Page 277: 59

$45x^2-56x-45$

Using $(a+b)(c+d)=ac+ad+bc+bd$ or the product of $2$ binomials, the given expression, $ (5x-9)(9x+5) $, is equivalent to \begin{array}{l}\require{cancel} 5x(9x)+5x(5)-9(9x)-9(5) \\\\= 45x^2+25x-81x-45 \\\\= 45x^2-56x-45 .\end{array}