1. 3.1 Exponential Functions
By Thersia Weber and Rachel Eron

2. Introduction

3. Exponential Format
Only an exponential function
if the x is in the exponent.
f(x) = abx a = initial amount b = rate of growth/base x = variable b > 1: exponential growth b < 1: exponential decay

4. Identifying Exponential Functions
f(x) = 3x
Exponential Function?
Initial Value?
Base?
Growth or Decay?
f(x) = 4x7
Exponential Function?
Initial Value?
Base?
Growth or Decay?
Yes
X is in exponent 1
A isn’t listed, automatically 1 3
B=3
Growth
B=3 > 1 No
X isn’t in exponent -

5. Table of Values a = x = 0 then plug it into y=abx Power y=6bx
then plug in another value on the table
3/2 = 6b1
solve for b
b= 3 . 1
2 6
b= 3 = 1
12 4
plug b into equation
y= 6(1/4)x
Power
x f(x)
-2 96
-1 24
0 6
1 3/2
2 3/8

6. Table of Values Examples
x f(x)
-2 108
-1 36
0 12
1 4
2 4/3
x f(x)
1900
4.8
1910
5.6
1920
6.5
1930
7.6
1940
7.9
1950
8.7
1960
10.1
1970
11.1
y = abx
y = 4.8bx
5.6 = 4.8b10
1.167 = b10
ln = 10 ln b
ln b = .0154
b = e.0154
y = 4.8 e.0154x
y = abx
y = 12bx
4 = 12b1
4/12 = b
4/12 = 1/3 = b
y = 12 (1/3)x
y = 12 (1/3)x
y = 4.8 e.0154x

7. Review of Graph Transformations
Graph transformations previously learned also apply to exponential functions
Horizontal Translations
y = abx-c graph shifts to right
y = abx+c graph shifts to left
Vertical Translations
y = abx +c graph shifts up
y = abx-c graph shifts down
Axis Flips
y = ab-x graph flips over y axis
y = -abx graph flips over x axis
Use URL to explore transformations of Exponential functions on graph
esource.dspView&ResourceID=104#

8. Plugging into Equations
Exponential equations can be found in many real life situations.
To solve real life equations, look at it as y = abx and find initial amount and other variables.
Plug in the numbers given and find the information asked for in problem.
The number B of bacteria in a petri dish culture of t hours is given by: B = 100e0.693t Find initial number of bacteria present. How many bacteria are present after 6 hours?
B = 100e0.693t
B = 100e0.693x6
B = 6394
Initial: 100
# Present after 6 hours: 6394

9. Allowance
Suppose your parents are going to pay you a weekly allowance for doing your household chores this coming year. Also, imagine that they are going to give you a choice of two payment schemes. With Choice A, your parents will pay you $10 every week. Therefore, you will have earned $10 after the first week, $20 after the second week, $30 after the third week, and so on. With Choice B, just to be nice, they are going to pay you $0.01 before you even start working. After you complete chores for week one, they will double your money, thus giving you a total of $0.02. After you complete chores for week two, they will once again double your money, thus giving you a total of $0.04. They will continue to double your money at the end of every week.
Write an equation for each payment scheme and use to make graphs. Explain which payment scheme you will choose and why using the graphs.
Each project will be turned in and graded according to rubric, worth 20 points.
Hyperlink rubric to word rubric

10. Allowance Answers
Each payment scheme will give you a fair amount of allowance, but judging by the graphs, the second payment plan would be a better choice because you will earn more eventually, faster.
2-3 groups to present explanation.
If present, 5 extra credit points.

11. References
Precalculus Textbook by Franklin Demana, Bert Waits, Bregory Foley, and Daniel Kennedy
(Graph, slide 10)
method=cResource.dspView&ResourceID=10 4# (Graphing Activity, slide 7)
ponential_growth.asp (Introduction Comic)
ds/US/Activities/Detail?id=7727 (Supplemental Activity, Allowance)

12. Quiz Now take a 10 question assessment on what you’ve learned.
Assessment Answers