## Elementary Algebra

$16a^2-56ab+49b^2$
Using $(a+b)^2=a^2+2ab+b^2$ or the square of a binomial, the given expression, $(4a-7b)^2 ,$ is equivalent to \begin{array}{l}\require{cancel} (4a)^2+2(4a)(-7b)+(-7b)^2 \\\\= 16a^2-56ab+49b^2 .\end{array}