5-4: Writing a Function Rule
**To write a function rule, look for a pattern relating the independent and dependent
values.
Example 1: Write a function rule for each table:
a. V = video rentals, C(V) = total cost
v
C(v)
1
5
2
6
3
7
4
8
b. S = side of the square; A(s) = area of the square.
s
A(s)
1
1
3
9
6
36
9
81
Team Work 1: Write a function rule for each table:
a.
n = number of candy bars
P(n) = Profit
n
P(n)
b.
x
y
1
-1
1
2
2
0
2
4
3
1
3
6
4
2
4
8
c. l = length; w= width
w
l
1
3
2
4
3
5
4
6
Example 2:
1. Kevin needs to develop a large scale model of his laptop design. He developed a model of
this laptop computer that is 5 times the size of the normal laptop computer.
a. Write a function rule to describe this relationship.
b. The spacebar on a normal laptop is 3½ inches long. Find the length of the spacebar
for the model.
2. A carpenter buys finishing nails by the pound. Each pound of nails costs $1.19.
a. Write a function rule to describe this relationship.
b. What would be the cost of 12 pounds of finishing nails?
Team Work 2:
Write a function rule for the area A(r) of a pond with radius r. Then, determine the
area of this pond if the radius should be 4 feet.
Example 3: Suppose you borrow $225 to buy a lawn mower. You charge $20 per yard you
mow. Write a rule to describe your profits, P(n), as a function of the number of lawns
mowed, n. Then determine the amount of profit you will earn from mowing 50 yards.
Team Work 3: Use the table below to answer the following questions.
a. Identify the independent and dependent variables.
Water Used for Laundry
b. Determine a function rule for the table.
c.
1 load
22 gallons
2 loads
44 gallons
3 loads
66 gallons
4 loads
88 gallons
How many gallons of water would you use for 7 loads of laundry?
Homework: Page 272 #2, 4, 6, 8, 10, 12, 14, 18, 26