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7.1 Graph Exponential Growth Functions
Name:__________________
Objective: To graph and use exponential growth functions.
Algebra 2 Standard 12.0
*An exponential function has the form y  ab x where a ≠ 0
and the base b is a positive number other than 1.
*If a > 0 and b> 1, then the function y  ab x is an exponential growth function
and b is called the _______________ factor.
* f  x   b x , where b > 1, is the parent function for exponential growth functions with base b.
The general shape of the graph is:
The x-axis is an
_____________________
of the graph. An asymptote
is a line that the graph
approaches more and
more closely, but not
actually touch.
The graph rises from left to right,
passing through the points (0 ,1)
and (1, b).
The domain of f  x   b x is all real numbers. The range is y > 0.
Ex. 1 Graph y  b x for b > 1.
Graph y  5 x
Step 1: Make a table
x -2 -1 0
1
y
2
3
Step 2: Plot the points from the table.
Step 3: Draw, from left to right, a smooth curve
that begins just above the x-axis, passes
through the plotted points and moves up.
* Transformation of Exponential Functions
f ( x)  b x


a  changes steepness :
y  a  b xh  k
a  1 stretches f(x) vertically.
0  a  1 shrinks f(x) vertically.
negative a reflects f(x) over the x-axis.

h  shifts left-right:
positive h shifts f(x) to the right
negative h shifts f(x) to the left

k  shifts up-down
positive k shifts f(x) up.
negative k shifts f(x) down.
The y-intercept of the graph of y  ab x occurs at (0, a), rather than (0, 1).
Alg 2 Adv. Ch. 7A Notes-page 1
Ex. 2 Graph y  ab x for b > 1. State the domain and range.
1
a) Graph y     3x
3
7
b) Graph y    
2
x
You Try: Graph the function. State the domain and range.
a) y  4 x
Ex. 3: Graph y  ab x h  k for b > 1
Graph y  2  4 x  2  1.
State the domain and range.
Alg 2 Adv. Ch. 7A Notes-page 2
1
b) y   3x
2
You Try: Graph y  3x 1  4 .
State the domain and range.
*Exponential Growth models: When a real-life quantity increases by a fixed percent each year
(or other time period), the amount y of the quantity after t years can be modeled by the equation
t
y  a 1  r 
where a is the initial amount and r is the percent increase expressed as a decimal.
The quantity (1+r) is the growth factor.
Ex. 4: in 1970, the population of Kern County, California was about 330,000. From 1970 to
2000, the county population grew at an average annual rate of about 2.4%.
 Write an exponential growth model giving the population P of Kern County t years after
1970. About how many people lived in Kern County in 1990?
*Compound Interest is the interest paid in an initial investment and on previously earned
interest. Consider an initial principal P deposited in an account that pays interest at an annual
rate r (expressed as a decimal), compounded n times per year.
nt
 r
The amount A in the account after t years is given by the equation: A  P  1   .
 n
Ex. 5: You deposit $5500 in an account that pays 3.6% annual interest. Find the balance after
2 years if the interest is compounded semiannually.
You Try: Find the balance if the interest is compounded monthly.
You Try: Estimate when the balance will be $6000 if the interest is compounded monthly.
Alg 2 Adv. Ch. 7A Notes-page 3
7-2
Graph Exponential Decay Functions
Name:__________________
Objective: To graph and use exponential decay functions
Algebra 2 Standard 12.0
*An exponential decay function has the form y  ab x where a >0 and 0 < b < 1.
The base b of an exponential decay function is called the _______________ factor.
* f  x   b x , where 0 < b < 1, is the parent function for exponential decay functions with base b.
The general shape of the graph is:
The graph falls from left to right,
passing through the points (0 ,1)
and (1, b).
The x-axis is an
asymptote of the graph.
The domain of f  x   b x is all real numbers. The range is y > 0.
Graph. Then state the domain, range and asymptote.
Ex. 1:
2
y  3 
3
x
You try: Graph.
Alg 2 Adv. Ch. 7A Notes-page 4
3
Ex. 2: y  2  
4
x
2
You Try: y  3  
5
x
Graph y  ab x h  k for 0 < b < 1
1
Ex. 3: y  2  
3
x2
1
Then state the domain, range and asymptote.
2
You Try: y  5  
3
x 1
2
*Exponential Decay models: When a real-life quantity decreases by a fixed percent each year
(or other time period), the amount y of the quantity after t years can be modeled by the equation
t
y  a 1  r 
where a is the initial amount and r is the percent decrease expressed as a decimal.
The quantity 1- r is the decay factor.
Ex. 4: A new car costs $25,000. The value of the car decreases by 15% each year. Write an
exponential decay model giving the car’s value y (in dollars) after t years. Estimate the value
after 4 years.
You Try: The value of a snowmobile has been decreasing by 7% each year since it was new.
After 3 years, the value is $3000. Find the original cost of the snowmobile.
Ex. 5: Describe the initial amount, growth/decay factor, and percent increase/decrease.
x
x
a) y  300 1.3
b) y  1000  0.4 
Alg 2 Adv. Ch. 7A Notes-page 5
7-3 Use Functions Involving e
Name:__________________
Objective: To study functions involving the natural base e.
Algebra 2 Standard 12.0
* The natural base e (the Euler number) is a special number like  or i.
n
 1
The expression 1   approaches e as n increases. (See Table on page 492)
 n
The natural base e is irrational number. It is defined as follows:
n
 1
As n approaches  , 1   approaches e  2.718281828 .
 n
Ex. 1: Simplify natural base expressions.
3
60e8
a. e9  e 6
b.
c.  10e 5 x 
3
12e
You Try:
a. 2e 3  6e5
b.
24e8
4e5
c. 10e 4 x 
Ex. 2: Evaluate natural base expressions.
Use a calculator to evaluate the expression. (Round to the nearest thousandths)
a. e6
b. e0.28
You Try: e
3
4
* Natural Base Functions: A function of the form y  ae is called the natural base exponential
ftn.
 If a > 0 and r > 0, the function is an exponential growth function.
 If a > 0 and r < 0, the function is an exponential decay function.
rx
x
x
* The graphs of the basic functions y  e and y  e are:
Note that the x-axis is an asymptote for the both graphs.
Ex. Graph natural base functions.
Graph the function. State the domain and range.
0.5 x
a. y  4e
b. y  e
You Try: Graph the function. State the domain and range.
Alg 2 Adv. Ch. 7A Notes-page 6
1.5 x  2 
4
3
0.5 x
a. y  2e
b. y  1.5e
0.25 x 1
2
0.15t
Ex. 4: Annual sales of a certain product can be modeled by the function S  60,000e
,
where S is the number of units sold and t is the number of years since the product went on the
market. Use the graphing calculator to estimate the annual sales 6 years after the product went
on the market.
*Continuously Compounded Interest: When interest is compounded continuously,
the amount A in an account after t years is given by the formula A  Pe
where P is the principal and r is the annual interest rate expressed as a decimal.
rt
Ex. 5: You deposit $3000 in an account that pays 2.5% annual interest compounded
continuously. What is the balance after 3 years?
You Try: You deposit $2500 in an account that pays 5% annual interest compounded
continuously.
a) Find the balance after 2 years.
B) When will the balance have doubled?
Alg 2 Adv. Ch. 7A Notes-page 7