Logarithm Change of Base Formula

A short discussion of the change of base formula for logarithms, presented in a way in which students can see where it comes from and why it might be useful. A useful version of the change of base formula is log_base A of B is equal to log B / log A or ln B / ln A. One reason that this is helpful is that many calculators only have a log of base 10 key or a log of base e key (natural log key). The change of base formula makes it possible to evaluate logarithms of any base by reformatting them as a quotient of common logarithms or a quotient of natural logarithms.