Question 38200
From 5x^2 - 20y^2, we first factor out the 5 and get
5(x^2 - 4y^2)
But x^2 - 4y^2 is the difference of squares, and can be factored again...
5(x^2 - 4y^2) =
5(x + 2y)(x - 2y)