1. 8.7 Exponential Decay Functions
Algebra 1
8.7 Exponential Decay Functions

2. y = C(1 – r)t EXPONENTIAL DECAY
A quantity is decreasing exponentially if it decreases by the same percent r in each unit of time t.
y = C(1 – r)t

3. y = C(1 – r)t
C is the initial amount (the amount before any decay occurs) r is the decay rate (as a decimal – must be greater than 0 and less than 1) t represents time

4. DECAY FACTOR
The expression (1 – r) is called the decay factor.

5. Write an Exponential Decay Model
Your friend bought a car for $ The car depreciates at the rate of 10% per year. Write an exponential decay model to represent the car’s value.

6. Write an Exponential Decay Model
You bought a computer for $1800. You expect the computer to lose value, or depreciate, at a rate of 29% per year. a) Write an exponential decay model to represent this situation. b) Find the value of the computer after 2 years. c) Graph the exponential decay model.

7. Compare Growth and Decay Models
Classify the model as exponential growth or exponential decay. Then identify the growth or decay factor.
y = (2)t y = (0.5)t
3. y = 5(0.2)t y = 0.7(1.1)t

8. Graph y = 5(0.2)t

9. Graph y = 0.7(1.1)t

10. The Difference of Growth and Decay
Explain the difference between a growth factor and a decay factor.