1. Warm Up
Which plan yields the most interest? Invest $100 Plan A: A 7.5% annual rate compounded monthly for 4 years Plan B: A 7.2% annual rate compounded daily for 4 years Plan C: A 7% annual rate compounded continuously for 4 years

2. Plan A: A 7.5% annual rate compounded monthly for 4 years
Which plan yields the most interest? Invest $100
Plan A: A 7.5% annual rate compounded monthly for 4 years
Plan B: A 7.2% annual rate compounded daily for 4 years
Plan C: A 7% annual rate compounded continuously for 4 years
𝟏𝟎𝟎𝟎 (𝟏+ .𝟎𝟕𝟓 𝟏𝟐 ) 𝟏𝟐∙𝟒 =𝟏𝟑𝟒𝟖.𝟔𝟎
𝟏𝟎𝟎𝟎 (𝟏+ .𝟎𝟕𝟐 𝟑𝟔𝟓 ) 𝟑𝟔𝟓∙𝟒 =𝟏𝟑𝟑𝟑.𝟕𝟐
𝟏𝟎𝟎𝟎 𝒆 .𝟎𝟕∙𝟒 =𝟏𝟑𝟐𝟑.𝟏𝟑

3. 5.5 Logarithmic Functions
Graph: 𝒚= 𝟐 𝒙
Graph the inverse.
Can you find the inverse equation algebraically?
𝒙= 𝟐 𝒚
The inverse equation is
𝒚= 𝒍𝒐𝒈 𝟐 𝒙

4. 5.5 Logarithmic Functions
𝑙𝑜𝑔 𝑏 𝑥=𝑎 ↔ 𝑏 𝑎 =𝑥
Example: If 𝟐 𝟑 =𝟖 then 𝒍𝒐𝒈 𝟐 𝟖=𝟑

5. 𝑙𝑜𝑔 𝑏 𝑥=𝑎 ↔ 𝑏 𝑎 =𝑥 a. 𝑙𝑜𝑔 12 1=0 a. 52=25 b. 2-3=1/8 b. 𝑙𝑜𝑔 27 3= 1 3
𝑙𝑜𝑔 𝑏 𝑥=𝑎 ↔ 𝑏 𝑎 =𝑥
Write each in exponential form.
a. 𝑙𝑜𝑔 12 1=0
b. 𝑙𝑜𝑔 27 3= 1 3
Write each in log form.
a. 52=25
b. 2-3=1/8
𝒍𝒐𝒈 𝟓 𝟐𝟓=𝟐
𝟏𝟐 𝟎 =𝟏
𝒍𝒐𝒈 𝟐 𝟏 𝟖 =−𝟑
𝟐𝟕 𝟏 𝟑 =𝟑

6. Evaluate without a calculator:=𝑥
𝒙=𝟐
𝟏𝟐 𝒙 =𝟏𝟒𝟒
𝑙𝑜𝑔
𝑙𝑜𝑔
𝑙𝑜𝑔 5 5 =𝑥
𝟏𝟎 𝒙 =.𝟎𝟎𝟏
𝒙=−𝟑
𝒙= 𝟏 𝟐 =𝑥
𝟓 𝒙 = 𝟓
Hint: set the expression equal to x.
Rewrite in exponential form and solve.

7. The Common Log Base 10 Written as log(x)
A logarithm can have any positive value as its base, but two log bases are more useful than the others.
The Common Log
Base 10
Written as log(x)
Base 10 is the default for logs
The log key on your calculator has base 10
Examples: pH (the measure of a substance's acidity or alkalinity), decibels (the measure of sound intensity), the Richter scale (the measure of earthquake intensity)

8. 𝒍 𝒏 𝒙 =𝒌 𝒆𝒌=𝒙 The Natural Log The other base that is used often is e
𝒍𝒐𝒈𝒆 𝒙 is usually written as 𝒍𝒏 𝒙
The natural log key on your calculator is LN
Just as the number e arises naturally in math and science, so does the natural log
𝒍 𝒏 𝒙 =𝒌 𝒆𝒌=𝒙

9. Find the value to the nearest hundredth:
a. 10 𝑥 =75 b. 𝑒 𝑥 =75
𝒙=𝒍𝒐𝒈𝟕𝟓 ≈𝟏.𝟖𝟖
𝒙=𝒍𝒏𝟕𝟓≈𝟒.𝟑𝟐

10. Solve Without a Calculator
𝑙𝑜𝑔𝑥=4
𝑙𝑛𝑥=2
𝑙𝑜𝑔 5 𝑥=2
𝑙𝑜𝑔 𝑥 121=2
𝑙𝑜𝑔 𝑥 =−1
10,000
𝑒 2 25 11 2

11. Page 194 Written Exercises #1-17 odds, #35-43 odds
Homework
Page 194 Written Exercises #1-17 odds, #35-43 odds

12. Quiz