exp(x) = summation(x^n/n!, n=0, inf)
Fair, infinite series are pretty esoteric. How about derivatives. The power rule:
d/dx x^n = n x^(n-1)
Eh maybe not, programmers don't use calculus that often. But surely statistics!
(1 + x)^n = summation((n choose k)x^k, k=0, n)
(1 + x)^n = (1 + 0)^0 = 1 = 0^0 = x^0 = x^0 + ... + x^n