Objectives:
Apply laws of logarithms to:
•
Simplify expressions
•
Solve equations
If

M and N are positive real #s and
b > 0 and ≠ 1, then:
Express

in terms of
Express

in terms of
Express

each in terms of log M
and log N:






log 45 – 2 log 3
(express as a single logarithm)

Simplify
Simplify
Simplify
Simplify:
If

f(x) = bx then f-1(x) = logb x

Therefore:

f-1(f(x)) = logb bx = x and
f(f-1(x)) = blogb x = x
This

means they “undo” each other.
Simplify:
Simplify:
Express

y in terms of x:
Express

y in terms of x:
Express

y in terms of x:
Solve:
Solve:
If

log9 5 = x and log9 4 = y, express
in terms of x and y:
log9 100

log9

36
If

log9 5 = x and log9 4 = y, express
in terms of x and y:
log9 3.2

5 6 laws of logarithms