Factor (x+9y)^2-16x^2y^2

Question

Tried several times have absolutly no clue

Answer 1

This is a difference of squares, since 16x²y²=(4xy)²

 

A difference of squares factors as a²-b²=(a+b)(a-b). In this problem, a=x+9y and b=4xy, so this comes out as

 

(x+9y+4xy)(x+9y-4xy)

 

I hope this helps.