Question

已知f(x)=log3x,求证f(x)+f(y)=f(xy)

急!!!!!!

Answer 1

f(x)+f(x0
=log3(x)++log3(y)
=log3(xy)
=f(xy)

追问

再问一题!拜托!
求证函数f(x)=lg[(1-x)/(1+x)] (-1<x<1) 是奇函数

追答

f(x)+f(-x)=0
所以是奇函数

Answer 2

这个证明不对啊，应该是f(x) + f(y) < f(xy) 啊
f(x) + f(y)
= log3x + log3y
= log(3x*3y)
= log(9xy)
= log3 + log(3xy)
< log(3xy)=f(xy)