Factor Theorem for Polynomials - Expii

If x-r is a factor of P(x), then P(r) = 0, so r is a root of P. The factor theorem says that all roots of P are "born" this way: in order for r to be a root, x-r must be a factor of P(x). That lets us think about factoring polynomials using Algebra 2 goggles.