Sometimes a logarithm is written without a base, like this: This usually means that the base is really 10. It is called a "common logarithm". Engineers love to use it. On a calculator it is the "log" button.

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For example the result for 2 x = 5 can be given as a logarithm, x = log 2 (5) . You will learn how to evaluate this logarithmic expression over the following lessons.

Logarithms are the inverses of exponents. They allow us to solve challenging exponential equations, and they are a good excuse to dive deeper into the relationship between a function and its inverse.

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