log(a)b=log(s)b/log(s)a
括号里的是底数
设log(s)b=M,log(s)a =N,log(a)b=R
则s^M=b,s^N=a,a^R=b
即(s^N)^R=a^R=b
s^(NR)=b
所以M=NR,即R=M/N,log(a)b=log(s)b/log(s)a