Answer
$49x^2+70xy+25y^2-4$
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: $[(7x+5y)-2][(7x+5y)+2]=(7x+5y)^2-(2)^2=(7x)^2+2\cdot 7x \cdot 5y+(5y)^2-4=49x^2+70xy+25y^2-4$