A logarithm is the inverse of an exponential function. The logarithm of a positive number m can be written as follows. The expression is read as
base b of m and states that raising b to the power yields m.
A common logarithm is a logarithm of base 10. For example, is equal to 3 because 103 is equal to 1000.
Since is used so often, it is sometimes written without a base. For positive values of m, the common of m can be defined as follows.