# How do you use the Change of Base Formula and a calculator to evaluate the logarithm log_15 7?

Feb 9, 2016

The change of base rule is: ${\log}_{a} n = \frac{\log n}{\log a}$

#### Explanation:

${\log}_{7} \left(15\right) = \frac{\log 15}{\log 7}$

Now that both logs are in base 10, you can evaluate using a regular scientific calculator by pressing the button labelled "log".