Calculators can evaluate base 10 logarithms. The change of base theorem, logb a = logc a / logc b, allows evaluating logarithms with non-base 10 bases by relating them to base 10 logarithms. Some useful properties of logarithms are that logb b = 1, logb b^y = y, and b^logb a = a. Students are assigned exercises 23 problems 1-13, 15-16, 18, and 20 to practice evaluating logarithms.

1. 1
 Calculators can evaluate base 10 logarithms.
 If you are asked to evaluate a logarithm without a base 10, the “Change of Base”
theorem is useful.
Change of Base Theorem
log 3
Example : log 2 3
log 2
Examples:
1. Evaluate log 2 17
Other Useful Properties
1. logb b 1
Proof:

2. 2
2. logb b y y
Proof:
3. blogb a a
Proof:
Try On Your Own
A) y log 2 42 B) 125log5 4 x
Assignment: Exercise 23 #1-13, 15, 16, 18, 20.
You will have time on Monday as well