8.3 Lesson
Logarithmic Functions
objectives:
 Students will learn how to write and evaluate logarithmic
expressions. Students will make a correlation between
mathematics and science with respect to concentrations, pH
and Richter Scale.
 Teacher will show students how to use technology to graph
their written logarithmic expression. Teacher will show
students how to relate the Richter Scale of 10 increments
and pH scale of the same increments.
Logarithmic Form
Exponential
Form
ex
X
logb y = x
2
log 5 25 = 2
Y=b
25 = 5
6
729 = 3
Logarithmic
Form
Logarithmic
Form
your turn …
Exponential
Form
Log 4 256 = 4
Logarithmic
Form
2
9 = 81
Log 2 32 = 5
Log 10 = 1
-1
8 =
1
8
Evaluating Logarithms
log 16
8
Log 16 = x
Write an equation in Logarithmic form
8
16 = 8
4
x
3x
2 = 2
Convert to Exponential form
Write each side using base 2
4 = 3x Set the exponents equal to each other
4
=X
3
Solve for X
Evaluate Logarithms
Log 8 16 = x
Log7 49
16 = 8
x
your turn…
Log -25
5
Log b y
Log 2
Y=b
-5
2
Log64
1
32
X