Answer
$9x^{2}-42xy+49y^{2}$
Work Step by Step
$(3x-7y)^{2}=(3x-7y)(3x-7y)$
To find the product of $(3x-7y)$ and $(3x-7y)$, we need to use the distributive property in which each term of the first polynomial is multiplied to each term of the second polynomial:
$(3x-7y)(3x-7y)$
=$3x(3x-7y)-7y(3x-7y)$
=$9x^{2}-21xy-21xy+49y^{2}$
=$9x^{2}-42xy+49y^{2}$
