College Algebra (6th Edition)

The change-of-base property for logarithms allows us to write logarithms with base $b$ in terms of a new base $a$. Introducing base $a$, the property states that $$\log_{b}M=\dfrac{\log_{a}M}{\log_{a}b}$$
The formula that defines the change of base formula is $\log_{b}M=\dfrac{\log_{a}M}{\log_{a}b}$