You may want to review linear equations first.

Suppose we have an equation with a polynomial on one side and 0
on the other. For example, we could have 2*x*^{2}
+ *x* = 0. It's not obvious how to solve this. But the
left-hand side factors as *x*(2*x* + 1). So the
solutions of the original equation are just the solution
of *x* = 0 and the solution of 2*x* + 1 = 0. These are 0
and −1 ⁄ 2. (It works because two
numbers multiply to 0 exactly when one or both of them is 0.)