Change of Base of Logarithm

Theorem
Let $\log_a x$ be the logarithm to base $a$ of $x$.

Then:
 * $\log_b x = \dfrac {\log_a x} {\log_a b}$

Thus a convenient formula for calculating the logarithm of a number to a different base.

Also presented as
Some people prefer to write this as:


 * $\log_a x = \log_a b \log_b x$

as it is delightfully easy to remember.