log掘族2 = log<判丛弊2>2/log<2>x = 1/log<2>xa=log<0.2>0.31/郑肆a =1/log<0.2>0.3 = log<0.3>0.2
a为底数用到一个公式loga(b)=lnb/衫裤肆纯凳lna a=log0.2(0.3)=ln0.3/ln0.21/或轿a=ln0.2/ln0.3=log0.3(0.2)