### Logarithms

**Note**:

- The logarithm of a negative number is not defined.
- log in the calculator denotes ${\mathrm{log}}_{10}$ or common logarithm.
- ${\mathrm{log}}_{10}$ may be written as lg.
- If the base is other than 10, the base should be specified, e.g. ${\mathrm{log}}_{3}81$