令 x = logA, y = logB, z=log(AB) 。2x = A, 2y = B, 2z = AB, 则有 2z = AB = (2x)^(2y) = 2x(2^y) ，有z = x*2y，即 log(AB) = BlogA。
log(A^B) = BlogA
原文：http://www.cnblogs.com/wbb2109/p/5538811.html
