Elementary Algebra

$49+84y+36y^2$
Using $(a+b)^2=a^2+2ab+b^2$, or the square of a binomial, the given expression, $(7+6y)^2 ,$ is equivalent to \begin{array}{l}\require{cancel} (7)^2+2(7)(6y)+(6y)^2 \\\\= 49+84y+36y^2 .\end{array}