Chapter 4 - Polynomials - 4.7 Polynomials in Several Variables - 4.7 Exercise Set - Page 284: 47

$x^2y^2+4xy-5$

Using $(a+b)(c+d)=ac+ad+bc+bd$ or the product of $2$ binomials, the given expression, $ (xy-1)(xy+5) ,$ simplifies to \begin{array}{l}\require{cancel} xy(xy)+xy(5)-1(xy)-1(5) \\\\= x^2y^2+5xy-xy-5 \\\\= x^2y^2+4xy-5 .\end{array}