# How do you evaluate log_3 81?

Feb 5, 2015

The answer is $4$ because ${3}^{4} = 81$

The question that the ${\log}_{a} x$ function is posing is:

To what power do I have take $a$ to get to $x$

So in your case the question is:

To what power do I take $3$ to reach $81$?

Usually, you will be working with '10-logs' or 'e-logs'.
Those you can find on your calculator:

${\log}_{10} = \log$-button and ${\log}_{e} = \ln$-button

If you use these buttons with shift or 2nd you get the opposite functions, the antilogs, marked as ${10}^{x}$ and ${e}^{x}$