Chapter 5 - Section 5.4 - Polynomials in Several Variables - Exercise Set - Page 376: 45

$4x^2+12xy+9y^2$

Using $(a\pm b)^2=a^2\pm2ab+b^2$ or the square of a binomial, the square of the given expression, $ (2x+3y)^2 ,$ is \begin{array}{l}\require{cancel} (2x)^2+2(2x)(3y)+(3y)^2 \\\\= 4x^2+12xy+9y^2 .\end{array}