Answer
$49x^6y^2-25x^2$
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: $(7x^3y+5x)(7x^3y-5x)=(7x^3y)^2-(5x)^2=49x^6y^2-25x^2$
