1) Quadratic Formula is like the swiss army knife when it comes to this. Never fails, but not convenient sometimes.
2) Consider the polynomial: x^2 + Ax + B = 0 Note that the leading coefficient is 1. Then you find two terms, say x1 and x2, whose product is B and sum is A. Then: x^2 + Ax + B = (x-x1)(x-x2) Sometimes, you just need a good hunting knife.
3) Consider the polynomial Ax^2 - k^2, such that A and k are real numbers. (A^2)(x^2) - k^2 = (Ax+k)(Ax-k)