2. CHAPTER 5: Exponential and Logarithmic Functions
5.1 Inverse Functions
5.2 Exponential Functions and Graphs
5.3 Logarithmic Functions and Graphs
5.4 Properties of Logarithmic Functions
5.5 Solving Exponential and Logarithmic Equations
5.6 Applications and Models: Growth and Decay; and Compound Interest
Copyright © 2012 Pearson Education, Inc. Publishing as Addison Wesley

3. 5.2 Exponential Functions and Graphs
Graph exponential equations and exponential functions.
Solve applied problems involving exponential functions and their graphs.
Copyright © 2012 Pearson Education, Inc. Publishing as Addison Wesley

4. Copyright © 2012 Pearson Education, Inc. Publishing as Addison Wesley
Exponential Function
The function f(x) = ax, where x is a real number, a > 0 and a  1, is called the exponential function, base a.
The base needs to be positive in order to avoid the complex numbers that would occur by taking even roots of negative numbers.
The following are examples of exponential functions:
Copyright © 2012 Pearson Education, Inc. Publishing as Addison Wesley

5. Graphing Exponential Functions
To graph an exponential function, follow the steps
listed:
1. Compute some function values and list the results in a table.
2. Plot the points and connect them with a smooth curve. Be sure to plot enough points to determine how steeply the curve rises.
Copyright © 2012 Pearson Education, Inc. Publishing as Addison Wesley

6. Copyright © 2012 Pearson Education, Inc. Publishing as Addison Wesley
Example
Graph the exponential function y = f (x) = 2x.
Copyright © 2012 Pearson Education, Inc. Publishing as Addison Wesley

7. Copyright © 2012 Pearson Education, Inc. Publishing as Addison Wesley
Example (continued)
As x increases, y increases without bound. As x decreases, y decreases getting close to 0; as x g -∞, y g 0.
The x-axis, or the line y = 0, is a horizontal
asymptote. As the x-inputs decrease, the curve gets closer and closer to this line, but does not cross it.
Copyright © 2012 Pearson Education, Inc. Publishing as Addison Wesley

8. Copyright © 2012 Pearson Education, Inc. Publishing as Addison Wesley
Example
Graph the exponential function
Note
This tells us the graph is the reflection of the graph of y = 2x across the y-axis. Selected points are listed in the table.
Copyright © 2012 Pearson Education, Inc. Publishing as Addison Wesley

9. Copyright © 2012 Pearson Education, Inc. Publishing as Addison Wesley
Example (continued)
As x increases, the function values decrease, getting closer and closer to 0. The x-axis, y = 0, is the horizontal asymptote. As x decreases, the function values increase without bound.
Copyright © 2012 Pearson Education, Inc. Publishing as Addison Wesley

10. Graphs of Exponential Functions
Observe the following graphs of exponential functions and look for patterns in them.
Copyright © 2012 Pearson Education, Inc. Publishing as Addison Wesley

11. Copyright © 2012 Pearson Education, Inc. Publishing as Addison Wesley
Example
Graph y = 2x – 2.
The graph is the graph of y = 2x shifted to right 2 units.
Copyright © 2012 Pearson Education, Inc. Publishing as Addison Wesley

12. Copyright © 2012 Pearson Education, Inc. Publishing as Addison Wesley
Example
Graph y = 5 – 0.5x .
The graph is a reflection of the graph of y = 2x across the y-axis, followed by a reflection across the x-axis and then a shift up 5 units.
Copyright © 2012 Pearson Education, Inc. Publishing as Addison Wesley

13. Copyright © 2012 Pearson Education, Inc. Publishing as Addison Wesley
Application
The amount of money A that a principal P will grow to after t years at interest rate r (in decimal form), compounded n times per year, is given by the formula
Copyright © 2012 Pearson Education, Inc. Publishing as Addison Wesley

14. Copyright © 2012 Pearson Education, Inc. Publishing as Addison Wesley
Example
Suppose that $100,000 is invested at 6.5% interest, compounded semiannually.
Find a function for the amount to which the investment grows after t years.
b) Find the amount of money in the account at t = 0, 4, 8, and 10 yr.
c) Graph the function.
Copyright © 2012 Pearson Education, Inc. Publishing as Addison Wesley

15. Copyright © 2012 Pearson Education, Inc. Publishing as Addison Wesley
Example (continued)
Solution:
a) Since P = $100,000, r = 6.5%=0.65, and n = 2, we can substitute these values and write the following function
Copyright © 2012 Pearson Education, Inc. Publishing as Addison Wesley

16. Copyright © 2012 Pearson Education, Inc. Publishing as Addison Wesley
Example (continued)
Solution continued:
b) We can calculate the values directly on a calculator.
Copyright © 2012 Pearson Education, Inc. Publishing as Addison Wesley

17. Copyright © 2012 Pearson Education, Inc. Publishing as Addison Wesley
Example (continued)
Solution continued:
c) Draw the graph.
Copyright © 2012 Pearson Education, Inc. Publishing as Addison Wesley

18. Copyright © 2012 Pearson Education, Inc. Publishing as Addison Wesley
The Number e
e is a very special number in mathematics. Leonard Euler named this number e. The decimal representation of the number e does not terminate or repeat; it is an irrational number that is a constant;
e  …
Copyright © 2012 Pearson Education, Inc. Publishing as Addison Wesley

19. Copyright © 2012 Pearson Education, Inc. Publishing as Addison Wesley
Example
Find each value of ex, to four decimal places, using the ex key on a calculator.
a) e3 b) e0.23
c) e2 d) e1
Solution:
a) e3 ≈
b) e0.23 ≈
c) e0 = 1
d) e1 ≈
Copyright © 2012 Pearson Education, Inc. Publishing as Addison Wesley

20. Graphs of Exponential Functions, Base e Example
Graph f (x) = ex and g(x) = e–x.
Use the calculator and enter y1 = ex and y2 = e–x. Enter numbers for x.
Copyright © 2012 Pearson Education, Inc. Publishing as Addison Wesley

21. Graphs of Exponential Functions, Base e - Example (continued)
The graph of g is a reflection of the graph of f across they-axis.
Copyright © 2012 Pearson Education, Inc. Publishing as Addison Wesley

22. Copyright © 2012 Pearson Education, Inc. Publishing as Addison Wesley
Example
Graph f (x) = ex + 3.
Solution: The graph f (x) = ex + 3 is a translation of the graph of y = ex left 3 units.
Copyright © 2012 Pearson Education, Inc. Publishing as Addison Wesley

23. Copyright © 2012 Pearson Education, Inc. Publishing as Addison Wesley
Example
Graph f (x) = e–0.5x.
Solution: The graph f (x) = e–0.5x is a horizontal stretching of the graph of y = ex followed by a reflection across the y-axis.
Copyright © 2012 Pearson Education, Inc. Publishing as Addison Wesley

24. Copyright © 2012 Pearson Education, Inc. Publishing as Addison Wesley
Example
Graph f (x) = 1  e2x.
Solution: The graph f (x) = 1  e2x is a horizontal
shrinking of the graph of y = ex followed by a reflection across the y-axis and then across the
x-axis, followed by a translation up 1 unit.
Copyright © 2012 Pearson Education, Inc. Publishing as Addison Wesley