We defined log functions as inverses of exponentials:
\begin{eqnarray*} y = \ln(x) &\Longleftrightarrow & x = e^y \cr
y = \log_a(x) & \Longleftrightarrow & x = a^y.
\end{eqnarray*}
Since we know how to differentiate exponentials, we can use implicit
differentiation to find the derivatives of
$\ln$ and $\log_a$. The videos below walk us through this process.