ALGEBRA 2
7.1 Graph Exponential Growth Functions
Goal  Graph and use exponential growth functions.
VOCABULARY
Exponential function
A function of the form y = abx where a  0 and the base b is a positive number other than one
Exponential growth function
A function of the form y = abx where a > 0 and b > 1
Growth factor
In a function of the form y = abx, b is the growth factor.
Asymptote
A line that a graph approaches more and more closely
PARENT FUNCTION FOR EXPONENTIAL GROWTH FUNCTIONS
The function y = bx, where b _>_ 1, is the parent function for the family of exponential growth functions with
base _b_. The general shape of the graph of y = bx is shown below.
The x-axis is an
asymptote of the
graph. An
asymptote is a line
that a graph
approaches more
and more closely.
The graph rises
from left to right,
passing through the
points (0,1) and
(1,b)
The domain of y = bx is _all real numbers_. The range is _y > 0_.
Example 1
Graph y = abx for b > 1
Graph the function
y  2x
Example 2
Graph y = abx  h + k for b > 1
Graph
y  2x 1  3 . State the domain and range.
Checkpoint Graph the function. State the domain and range.
1.
y  2 x
x 1
2. y  3  3
x
3. y  3 2
Exponential Growth Models
y  a (1  r )t
a  initial amount
(1  r )  growth factor
Example 3
Solve a multi-step problem
Buffalo In the last 12 years, an initial population of 38 buffalo in a state park grew by about 7% per year.
a. Write an exponential growth model giving the number n of buffalo after t years. About how many buffalo
were in the park after 7 years?
b. Graph the model. Use the graph to estimate the year when there were about 53 buffalo.
COMPOUND 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. The amount A in the account after t years is given by this equation:
A=
 r
P 1  
 n
nt
Example 4
Find the balance in an account
You deposit $2900 in an account that pays 3.5% annual interest. Find the balance after 1 year if the
interest is compounded monthly and annually.
a. With interest compounded monthly, the balance after 1 year is:
b. With interest compounded annually, the balance after 1 year is:
Checkpoint Complete the following exercises.
2. From Example 3, how many buffalo were in the park after 11 years?
3. You deposit $5000 into an account that pays 3.72% annual interest. Find the balance after three years if
the interest is compounded quarterly.
7.2 Graph Exponential Decay Functions
Goal  Graph and use exponential decay functions.
VOCABULARY
Exponential decay function
A function of the form y = abx where a > 0 and 0 < b< 1
Decay factor
In a function of the form y = abx, the base b is the decay factor.
PARENT FUNCTION FOR EXPONENTIAL DECAY FUNCTIONS
The function y = bx, where 0 < b < 1, is the parent function for the family of exponential decay functions with
base b. The general shape of the graph of y = bx is shown below.
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 y = bx is _all real numbers_. The range is _y > 0_.
Example 1
Graph y = abx for 0 < b < 1
Graph the function
x
1
y  .
2
Example 2
Graph y = abx  h + k for 0 < b < 1
1
Graph y   
3
x 1
 1 State the domain and range.
Checkpoint Graph the function. State the domain and range.
1
1. y  2  2 
 
x
x
2.
1
y  3   2
2
Exponential Decay Formula
y = a(l  r)t
Example 3
Solve a multi-step problem
Televisions A new television costs $1200. The value of the television decreases by 21% each year. Write an
exponential decay model giving the television's value y (in dollars) after t years. Estimate the value after 2
years. Graph the model. Use the graph to estimate when the value of the television will be $300.
Checkpoint Complete the following exercise.
3. Rework Example 3, with a 12% decrease each year.
7.3 Use Functions Involving e
Goal  Study functions involving the natural base e.
VOCABULARY
Natural base e
n
1


An irrational number, where 1   approaches e as n increases
n

THE NATURAL BASE e
The natural base e is irrational. It is defined as follows:
n
1
As n approaches   1   approaches
n

e  _2.718281828_.
Example 1
Simplify natural base expressions
Simplify the expression.
a. e6  e3 
6
b. 18e 
4
2e
c. (4e3x)2 
Example 2
Evaluate natural base expressions
Use a calculator to evaluate the expression.
Expression
a. e2
b.e0..3
Checkpoint Complete the following exercises.
1. Simplify e3  e6.
2. Simplify
(4e3)2
.
8e5
Use a calculator to evaluate the expression.
3. e4
4. e0.36
NATURAL BASE FUNCTIONS
A function of the form y  aerx is called a natural base exponential function.

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.
Example 3
Graph natural base functions
Graph the function. State the domain and range.
a. y  e x
b.
y  2e x
Checkpoint Graph the function. State the domain and range.
5.
y  e x 1  3
CONTINUOUSLY COMPOUNDED INTEREST
When interest is compounded continuously, the amount A in an account after t years is given by the formula
A  _Pert_
where P is the _principal_ and
t is the _annual interest rate_ expressed as a decimal.
Example 4
Model continuously compounded interest
Compound Interest You deposit $3500 in an account that pays 4% annual interest compounded continuously.
What is the balance after 1 year?
Checkpoint Complete the following exercise.
6. You deposit $4800 in an account that pays 6.5% annual interest compounded continuously. What is the
balance after 3 years?
7.4 Evaluate Logarithms and Graph Logarithmic Functions
Goal  Evaluate logarithms and graph logarithmic functions.
VOCABULARY
Logarithm of y with base b
A logarithm denoted by logb y and defined as logb y = x if and only if bx = y, given that b and y are positive
numbers with b  1.
Common logarithm
A logarithm with base 10
Natural logarithm
A logarithm with base e
DEFINITION OF LOGARITHM WITH BASE b
Let b and y be positive numbers with b  1. The logarithm of y with base b is denoted by logb y is defined as
follows:
logb y = _x_ if and only if bx = _y_
The expression logb y is read as "log base b of y."
Example 1
Rewrite logarithmic equations
Logarithmic Form
a. log2 32 = 5
b. log7 1 = 0
c. log13 13 = 1
d. log1/2 2 = 1
Exponential Form
Checkpoint Rewrite the equation in exponential form.
1. log18 1 = 0
2. log2 64 = 6
Example 2
Evaluate logarithms
Evaluate the logarithm.
a. log3 81
b. log5 1
c. log 4 64
d. log 2 32
e. log49 7
f. log4 0.25
g. log1/4 256
Checkpoint Evaluate the logarithm.
3. log1/3 9
4. log16 4
Example 3
Use calculator
a. log 2.4
b. ln 5
Example 4
Use inverse properties
Simplify the expression.
a. 10log 6.7
b. log2 16x
Example 4
Find inverse functions
Find the inverse of the function
a. y = log3/2 x
b. y = In(x  4)
Checkpoint Complete the following exercises.
5. Simplify 10log 7x.
6. Simplify log3 27x.
Find the inverse of the function.
7. y = 72x
8. y = In(x + 6)
PARENT GRAPHS FOR LOGARITHMIC FUNCTIONS
The graph of y = logb x is shown below for b > 1 and for 0 < b < 1.
Because y = logb x and y = bx are __inverse__ functions, the graph of y = logb x is the reflection of the graph of y
= bx in the line __y = x__.
Note that the y-axis is a vertical asymptote of the graph of y = logb x. The domain of y = logb x is _x > 0_ , and
the range is __all real numbers__ .
Example 5
Graph logarithmic functions
Graph
a) y = log2 x
b)
y  log3 x  2
Example 6
Translate a logarithmic graph
Graph y = log3(x + 3) + 2. State the domain and range.
Checkpoint Graph the function. State the domain and range.
9. y  log 2 ( x  2)  3
7.5 Apply Properties of Logarithms
Goal  Rewrite logarithmic expressions.
PROPERTIES OF LOGARITHMS
Let b, m, and n be positive numbers such that b  1
Product Property
logb mn = logb m _+__ logb __n__
Quotient Property
logb m = logb m _____ logb _ n __
n
Power Property
logb mn = __n logb m_
Example 1
Use properties of logarithms
Use log5 4  0.861 and log5 9  1.365 to evaluate the logarithm.
a. log5 4 =
9
b. log5 36 =
c. log5 81 =
Checkpoint Use log3 2  0.6309 and log3 8  1.8928 to evaluate the logarithm.
1. log3 4
2. log3 16
Example 2
Expand a logarithmic expression
2
Expand log3 7x
y
.
Example 3
Condense a logarithmic expression
Condense log 2 + 3 log 3  log 9.
Checkpoint Complete the following exercises.
3. Expand log
7 y3
.
4x 2
4. Condense In 3 +2 In x In y.
CHANGE OF BASE FORMULA
If a, b, and c are positive numbers with b  1 and c  1, then
logc a = log a
b
logb c
log b a
In a .
In particular logc a = ________
and logc a = _______
log b c
In c
Example 4
Use the change-of-base formula
Evaluate log6 11 using common logarithms and natural logarithms.
Checkpoint Use the change-of-base formula to evaluate the logarithm.
5. log16 26
6. log5 13
7.6 Solve Exponential and Logarithmic Equations
Goal  Solve exponential and logarithmic equations.
VOCABULARY
Exponential equation
An equation in which variable expressions occur as exponents
Logarithmic equation
An equation that involves logarithms of variable expressions
PROPERTY OF EQUALITY FOR EXPONENTIAL EQUATIONS
Algebra
If b is a positive number other than 1, then bx = by if and only if _x = y_ .
Example
If 5x = 54, then x = 4. If x = _4_, then 5x = 54.
Example 1
Solve by equating exponents
Solve 64x = 16x + 1.
Example 2
Take a logarithm of each side
Solve 6x = 27.
Example 3
You deposit $1000 in an account that pays 4% annual interest. How long will it take for
the balance to reach $5000 for each given frequency ofcompounding?
a) Quarterly
b) Continuosly
Checkpoint Solve the equation.
1. 37x  3 = 92x
2. 5x = 72
3. 83x + 2  6 = 5
4. You deposit $500 in an account that pays 5% annual interest. How long will it take for the
balance to reach $10,000 if interest is compounded monthly?
Example 4
Take a logarithm of each side
Solve 6e0.25x + 8 = 20
Checkpoint Solve the equation.
5. 3e0.5x + 2 = 5
PROPERTY OF EQUALITY FOR LOGARITHMIC EQUATIONS
Algebra
If b, x, and y are positive numbers with b  1,
then logb x = logb y if and only if _x = y .
Example
If log3 x = log3 8, then x = 8. If x = _8_, then log3 x = log3 8.
Example 5
Solve a logarithmic equation
Solve log7(6x  16) = log7(x  1)
Example 5
Exponentiate each side of an equation
Solve log5(3x  8) = 2.
Example 6
Check for extraneous solutions
Solve log 5x + log(x  1) = 2.
Checkpoint Solve the equation. Check for extraneous solutions.
6.In(7x  13) = In(2x + 17)
7.log3(2x + 9) = 3
8.log4(10x + 624) = 5
9. log 6(x  9) + log6 x=2