1. Writing Exponential Growth Functions
8.5
Writing Exponential Growth Functions
Objective
I will use the equation for exponential growth to find resulting balances.
Key Words
exponential function
growth factor
growth rate

2. 8.5 Exponential Growth Functions
C is initial amount
t is the time period
r is the growth rate
Exponential Growth - growth in which a quantity increases by the same percent in each unit of time
Growth Factor - (1 + r); how much growth there is total; original amount plus percent increase
Growth Rate - r; how much growth there is in addition to the original amount; percent increase

3. 8.5 Exponential Growth Functions
Use the exponential growth model to find the account balance.
1. A principal of $450 is deposited in an account that pays 2.5% interest compounded yearly. Find the account balance after 2 years.
Method 1: Solve a simpler problem
Original balance increases 2.5% per year, so growth factor is 102.5% or 1.025
Year 1
Year 2
The account balance will be about $ after two years.

4. 8.5 Exponential Growth Functions
Use the exponential growth model to find the account balance.
1. A principal of $450 is deposited in an account that pays 2.5% interest compounded yearly. Find the account balance after 2 years.
Method 2: Use the formula
Equation
Substitute
Add
Exponent
Multiply
The account balance will be about $ after two years.

5. 8.5 Exponential Growth Functions
C is initial amount
t is the time period
r is the growth rate
Guided Practice: Use the exponential growth model to find the account balance.
2. A principal of $800 is deposited in an account that pays 3% interest compounded yearly Find the account balance after 5 years.

6. Guided Practice: Finding an Initial Investment
3. How much must you deposit in an account that pays 4% interest compounded yearly to have a balance of $2000 after 5 years?
Exponential Growth

7. Writing an Exponential Growth Model
4. A population of 50 pheasants is released in a wildlife reserve. The population triples each year for 3 years. What is the population after 3 years?
Population Triples - Growth Factor = 3
Growth Factor = 1 + r
3 = 1 + r
r = 2
There will be 1350 pheasants after 3 years.

8. Graphing an Exponential Growth Function
Graph like any other exponential function
Make a table of values
Input x-values into the exponential growth function equation - y = C(1 + r)t
How many values? 5

9. x y 5. Graph the exponential growth model in Exercise 3. 5000 4000
3000
2000
1000

10. Guided Practice
Richard opens a bank account with $1000 that pays a 4% interest rate. Write an exponential growth function to find the amount of money in the account after t years. Then graph the function.
x y

11. Independent Practice
A pack of wolves starts with 8 wolves. The number of wolves in the pack doubles each year. Write an exponential growth function to represent the situation. Then graph the function to find how many wolves will be in the pack after 4 years.