# Proving a log identity

1. Mar 20, 2013

### K29

1. The problem statement, all variables and given/known data

$a^{log_{b}(c)}=c^{log_{b}(a)}$

3. The attempt at a solution
Take $log_{a}$ of both sides:
$log_{a}(a^{log_{b}(c)})=log_{a}(c^{log_{b}(a)})$

gives:
$log_{b}c=log_{b}alog_{a}c$

Looks like one more step for the RHS. I sort of see that the RHS should become $log_{b}c$ and then we'll be done. But standard log laws don't seem to help me make this step. Please help with this step/explain why this is so?

2. Mar 20, 2013

### SammyS

Staff Emeritus
Using the commutative law of multiplication, the RHS is $\displaystyle \ (\log_{a\,}c)\,(\log_{b\,}a)\quad\to\quad\log_{b\,}\left(a^{\log_{a\,}c}\right)$

3. Mar 20, 2013

### K29

Got it. Thanks a bunch