# Logarithms 14 - Change of Base

Taught by YourMathGal
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Lesson Summary:

In this lesson, we learn about the change of base formula for logarithms. We are shown how to use this formula to solve for unknown variables in logarithmic equations with bases that we may not have a logarithm function for on our calculator. The formula is log a over log b, and we are given several examples to practice with and check our answers on our calculator.

Lesson Description:

Develops and uses the change of base formula for logs. .

More free YouTube videos by Julie Harland are organized at http://yourmathgal.com

• What is the change of base formula for logarithms?
• How can you use the change of base formula for logarithms?
• How do you derive the change of base formula for logs?
• Why does the change of base formula for logarithms work?
• How can you evaluate log base 2 of 11 using the change of base formula and a calculator?
• How can you evaluate log base 3 of 20 using the change of base formula and a calculator?
• How can you evaluate log base 1/2 of 18 using the change of base formula and a calculator?
• How can you evaluate log base 4 of 5/6 using the change of base formula and a calculator?
• How can you check your answer to a change of base logarithm problem?
• #### Staff Review

• Currently 4.0/5 Stars.
This lesson explains the very important change of base formula for logarithms. It is derived and explained, and then it is used to simplify / evaluate several example problems. Because calculators can only compute logarithms for base 10 or base e, the change of base formula is very useful for computing logarithms for other bases. All steps are shown and explained along with a way of checking your solution.