## Key Equations

 The Product Rule for Logarithms ${\mathrm{log}}_{b}\left(MN\right)={\mathrm{log}}_{b}\left(M\right)+{\mathrm{log}}_{b}\left(N\right)$ The Quotient Rule for Logarithms ${\mathrm{log}}_{b}\left(\frac{M}{N}\right)={\mathrm{log}}_{b}M-{\mathrm{log}}_{b}N$ The Power Rule for Logarithms ${\mathrm{log}}_{b}\left({M}^{n}\right)=n{\mathrm{log}}_{b}M$ The Change-of-Base Formula ${\mathrm{log}}_{b}M\text{=}\frac{{\mathrm{log}}_{n}M}{{\mathrm{log}}_{n}b}\text{ }n>0,n\ne 1,b\ne 1$

## Key Concepts

• We can use the product rule of logarithms to rewrite the log of a product as a sum of logarithms.
• We can use the quotient rule of logarithms to rewrite the log of a quotient as a difference of logarithms.
• We can use the power rule for logarithms to rewrite the log of a power as the product of the exponent and the log of its base.
• We can use the product rule, quotient rule, and power rule together to combine or expand a logarithm with a complex input.
• The rules of logarithms can also be used to condense sums, differences, and products with the same base as a single logarithm.
• We can convert a logarithm with any base to a quotient of logarithms with any other base using the change-of-base formula.
• The change-of-base formula is often used to rewrite a logarithm with a base other than 10 or $e$ as the quotient of natural or common logs. A calculator can then be used to evaluate it.

## Glossary

change-of-base formula
a formula for converting a logarithm with any base to a quotient of logarithms with any other base
power rule for logarithms
a rule of logarithms that states that the log of a power is equal to the product of the exponent and the log of its base
product rule for logarithms
a rule of logarithms that states that the log of a product is equal to a sum of logarithms
quotient rule for logarithms
a rule of logarithms that states that the log of a quotient is equal to a difference of logarithms

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