When do you use the difference of squares?
When you hae a square expression like 16y^2 and another square expression like 9x^2
You are finding the difference between them 16y^2 - 9x^2
And you want to factorize the expression. That means one expression multiplied by another expression.
\(\sqrt{16y^2}=4y\\ \sqrt{9x^2}=3x\\ 16y^2-9x^2=(4y+3x)(4y-3x)\)