Answer
$25x^2+70xy+49y^2-4$
Work Step by Step
The product of a binomial sum and a binomial difference is: $(A+B)(A-B)=A^2-B^2$.
The square of a binomial sum is: $(A+B)^2=A^2+2AB+B^2$.
The square of a binomial difference is: $(A-B)^2=A^2-2AB+B^2$.
Hence here: $[(5x+7y)-2][(5x+7y)+2]=(5x+7y)^2-(2)^2=(5x)^2+2\cdot 5x \cdot 7y+(7y)^2-4=25x^2+70xy+49y^2-4$