1. Writing a Function Rule
ALGEBRA 1 LESSON 5-4
(For help, go to Lesson 5-3.)
Model each rule with a table of values.
1. f(x) = 5x – 1 2. y = –3x g(t) = 0.2t – 7
4. y = 4x f(x) = 6 – x 6. c(d) = d + 0.9
Evaluate each function rule for n = 2.
7. A(n) = 2n – 1 8. f(n) = –3 + n – 1 9. g(n) = 6 – n
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2. Writing a Function Rule
ALGEBRA 1 LESSON 5-4
Solutions 1. 2. 3. 4. 5. 6.
5-4

3. Writing a Function Rule
ALGEBRA 1 LESSON 5-4
Solutions (continued)
7. A(n) = 2n – 1 for n = 2:
A(2) = 2(2) – 1 = 4 – 1 = 3
8. f(n) = –3 + n – 1 for n = 2:
f(2) = –3 + 2 – 1 = –1 – 1 = –2
9. g(n) = 6 – n for n = 2:
g(2) = 6 – 2 = 4
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4. Writing a Function Rule
ALGEBRA 1 LESSON 5-4
Write a function rule for each table.
x ƒ(x)
2 8
4 10
6 12
8 14 a.
Ask yourself, “What can I do to 2 to get 8, 4 to get 10, ...?”
You add 6 to each x-value to get the ƒ(x) value.
Relate:    equals plus 6
Write: =
ƒ(x) x
A rule for the function is ƒ(x) = x + 6.
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5. Writing a Function Rule
ALGEBRA 1 LESSON 5-4
(continued) b.
x y
1 2
2 5
3 10
4 17
Ask yourself, “What can I do to 1 to get 2, 2 to get 5, ?”
You multiply each x-value times itself and add 1 to get the y value.
Relate:    equals plus 1
Write: = x2 y
x times itself
A rule for the function is y = x2 + 1.
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6. Writing a Function Rule
ALGEBRA 1 LESSON 5-4
The journalism class makes $25 per page of advertising in the yearbook. If the class sells n pages, how much money will it earn?
a. Write a function rule to describe this relationship.
Relate:    is  25  times  
money earned
number of pages sold
Define: Let = number of pages sold. n
Let = money earned.
P(n)
Write: = 25 •
The function rule P(n) = 25n describes the relationship between the number of pages sold and the money earned.
5-4

7. Writing a Function Rule
ALGEBRA 1 LESSON 5-4
(continued)
b. The class sold 6 pages of advertising. How much money did the class make?
P(6) = 25 • 6 Substitute 6 for n.
P(6) = 150 Simplify.
P(n) = 25 • n
The class made $150.
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8. Writing a Function Rule
ALGEBRA 1 LESSON 5-4
The choir spent $100 producing audio tapes of its last performance and will sell the tapes for $5.50 each. Write a rule to describe the choir’s profit as a function of the number of tapes sold.
Relate: is $5.50 times minus cost of tape production
total profit
tapes sold
Define: Let = number of tapes sold. t
Let = total profit.
P(t)
Write: = • – 100
The function rule P(t) = 5.5t – 100 describes the profit as a function of the number of tapes sold.
5-4

9. Writing a Function Rule
ALGEBRA 1 LESSON 5-4
1. Write a function rule for each table.
x y
–1 –5
0 0
1 5
2 10 a.
x ƒ(x)
–1 –4
0 –3
1 –2
2 –1 b.
y = 5x
ƒ(x) = x – 3
2. Write a function rule to describe each relationship.
a. the total cost T(c) of c pounds of apples at $.82 a pound
b. a scale model s of a moth m that is 6 times the actual size of the moth
T(c) = 0.82c
s(m) = 6m
3. You borrow $60 to buy a bread-making machine. You charge customers $1.50 a loaf for your special bread. Write a rule to describe your profit as a function of the number n of loaves sold.
P(n) = 1.5n - 60
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