- not only is the formula
exp(x) = ∑xⁿ/n!
illegitimate at x = 0 unless you define 0⁰ = 0, the binomial formula
(x+y)ⁿ = ∑_{i=0}^n (n choose i) xⁱ yⁿ⁻ⁱ
doesn't make sense when x = 0 or y = 0 unless 0⁰ = 0. We need this convention for a lot of math.
