Integration by parts is a technique of integration applicable to integrands consisting of a product that cannot be rewritten as one or more easily integrated terms — at least, not without difficulty. The technique is particularly useful in cases containing a product of algebraic and transcendental factors.
The fundamental theorem of algebra states that if P(x) is a polynomial of degree n then P(x) can be factored into linear factors over the complex numbers. Furthermore, P(x) can be factored over the real numbers as a product of linear and quadratic terms.