Question 77412
*[invoke quadratic_factoring 25, 0, -81]

Now introduce the y term into the factorization:

{{{(5x+9y)(5x-9y)}}}

So in other words, {{{25x^2 - 81y^2}}} factors to 

{{{(5x+9y)(5x-9y)}}}

Note: this binomial is a perfect square. All perfect squares of the form

{{{x^2-y^2}}}

factor to

{{{(sqrt(x)+sqrt(y))(sqrt(x)-sqrt(y))}}}