对任意x>0,都有log 0.2 x=

Question

如题所述

Answer 1

log0.2(x)=ln(x)/ln(0.2)=-1*ln(x)/ln(5)=ln(x^-1)/ln5=log5(1/x)
其中这里用到换底公式：log n (m)=log a (m)/log a (n)
还用到以下性质：a*log n (m)=log n (m^a)