f(x^3)=lgx(x>0)求f(x)

题目

f(x^3)=lgx(x>0)求f(x)

答案

f(x^3) = lg x
let y =x^3
f(y) = lg y^(1/3) = (1/3)lgy
ie
f(x) = (1/3) lgx