Lesson 8.6 – Write and Graph Exponential Decay Recall: A table ...

Lesson 8.6 – Write and Graph Exponential Decay Recall: A table represents an exponential function

if the values of

are multiplied by

times

every time the -values increase by 1.

The graph of exponential growth rises from left to right. The function

Exponential decay – when the exponential function

has

and

has:

The graph of an exponential decay function falls from left to right. Write a rule for the function.

Tell whether the graph represents exponential growth or exponential decay. Then write a rule for the function.

When a quantity decays exponentially, it decreases by the same percent over equal time periods. It can be modeled as the following:

A farmer bought a tractor in 1999 for $30,000. The value has been decreasing at a rate of 18% per year. a) Write a function that models the value of the tractor over time. b) What was the approximate value of the tractor in 2005?

You purchase a cell phone for $125. The value of the cell phone decreases by about 20% annually. a) Write a function that models the value of the cell phone over time.

b) Find the value of the cell phone after 3 years.