1. 3.4 Writing Exponential
Functions

2. Writing Functions from Graphs
•Use points from the graph to make a
table.
•Identify y-int (0, a) and growth factor b
•Write equation: y = a(b)x

3. Example 1:
•Write an equation of the function
shown:

4. Example 2:
•Write an equation of the function
shown:

5. You Try!
•Write an equation of the function
shown:

6. Writing Equations from Stories
1. Identify the starting value a and
growth/decay factor b.
2. Write equation y = a(b)x

7. Example 1:
•You bake 100 cookies for a bake sale
and sell half of them every hour.

8. You Try!
•You get four hamsters for Christmas
and the hamster population doubles
every month.

9. Growth/Decay as a %
•When the change is given as a %:
•Write the percent as a decimal  r
▫ (divide by 100)
•For growth: b = 1 + r
•For decay: b = 1 – r

10. Example 2:
•You buy an antique table for $525.
Each year the value increases by 5%.

11. Example 3:
•You buy a new car for $24,000. The
value of the car decreases by 16%
each year.

12. You Try!
•You buy a stereo system for $780.
Each year the value decreases by
6%.

13. Writing Verbal Descriptions
•Use the a and b values from the
equation to write a story for the
function.
•For growth: r = b – 1
•For decay: r = 1 – b
•Then write as a % in the story.

14. Example 4:
• y = 6(2)x

15. Example 5:
• f(t) = 500(1.03)t

16. Example 6:
• g(t) = 90(.75)t

17. You Try!
• Write a story for:
• y = 25(1.2)x
• C(t) = 21500(0.88)t