Elementary and Intermediate Algebra: Concepts & Applications (6th Edition)

$x^2+24x+144$
Using $(a+b)^2=a^2+2ab+b^2$ or the square of a binomial, the given expression, $(x+12)(x+12)$, is equivalent to \begin{array}{l}\require{cancel} (x+12)^2 \\\\= (x)^2+2(x)(12)+(12)^2 \\\\= x^2+24x+144 .\end{array}