Math — Binomial Series

(1+x)^n = 1 + nx + \frac{n(n-1)}{2!}x^2 + \cdots

|x| < 1

(1+x)^{-1} = 1 - x + x^2 - x^3 + \cdots

(1+x)^{1/2} = 1 + \tfrac{1}{2}x - \tfrac{1}{8}x^2 + \cdots