## Elementary Algebra

$4x^2+20xy+25y^2$
Using $(a+b)^2=a^2+2ab+b^2$, or the square of a binomial, the given expression, $(2x+5y)^2 ,$ is equivalent to \begin{array}{l}\require{cancel} (2x)^2+2(2x)(5y)+(5y)^2 \\\\= 4x^2+20xy+25y^2 .\end{array}