How do you convert a logarithm from one base to another? It turns out that loga(x) = loga(b) log_b(x). One way to remember this: think of the b's "cancelling" on the right. To see why it's true, start by writing b = a^m and x = b^n, so x = (a^m)^n = a^(mn) by the power rule for exponents.