Question

How do you factor `y^2+2xy - 63x^2`?

Answer 1

Notice that `63 = 9 xx 7` and `2 = 9 - 7`, so

`y^2+2xy-63x^2 = (y-7x)(y+9x)`

When the coefficient of the first term in one of these quadratics is `1`, look for factors of the coefficient of the last term, whose sum or difference is the middle coefficient.