1. 12-2 Rational Functions Warm Up Lesson Presentation Lesson Quiz
Holt Algebra 1

2. Warm Up
The inverse variation xy = 8 relates the constant speed x in mi/h to the time y in hours that it takes to travel 8 miles. Graph this inverse variation. Then use the graph to estimate how many hours it would take to travel 8 miles jogging at a speed of 4.5 mi/h.
Possible answer: 1 h 45 min

3. Objectives Identify excluded values of rational functions.
Graph rational functions.

4. Vocabulary rational function excluded value discontinuous function
asymptote

5. A rational function is a function whose rule is a quotient of polynomials in which the denominator has a degree of at least 1. In other words, there must be a variable in the denominator. The inverse variations you studied in the previous lesson are a special type of rational function.
Rational functions:
Not rational functions:

6. For any function involving x and y, an excluded value is any x-value that makes the function value y undefined. For a rational function, an excluded value is any value that makes the denominator equal to 0.

7. Example 1: Identifying Excluded Values
Identify the excluded value for each rational function. A.
x = 0
Set the denominator equal to 0.
The excluded value is 0. B.
x – 2 = 0
Set the denominator equal to 0.
x = 2
Solve for x.
The excluded value is 2.

8. Check It Out! Example 1
Identify the excluded value for each rational function. a.
x = 0
Set the denominator equal to 0.
The excluded value is 0. b.
x – 1 = 0
Set the denominator equal to 0.
x = 1
Solve for x.
The excluded value is 1.

9. Check It Out! Example 1
Identify the excluded value for each rational function. c.
x + 4 = 0
Set the denominator equal to 0.
x = –4
Solve for x.
The excluded value is –4.

10. Most rational functions are discontinuous functions, meaning their graphs contain one or more jumps, breaks, or holes. This occurs at an excluded value.
One place that a graph of a rational function is discontinuous is at an asymptote. An asymptote is a line that a graph gets closer to as the absolute value of a variable increases. In the graph shown, both the x- and y-axes are asymptotes. The graphs of rational functions will
get closer and closer to but never
touch the asymptotes.

11. For rational functions, vertical asymptotes will occur at excluded values.
Look at the graph of y = The denominator is 0 when x = 0 so 0 is an excluded value. This means there is a vertical asymptote at x = 0. Notice the horizontal asymptote at y = 0.

12. Vertical lines are written in the form x = b, and horizontal lines are written in the form y = c.
Writing Math

13. Look at the graph of y = Notice that the graph of the parent function y= has been translated 3 units right and there is a vertical asymptote at x = 3. The graph has also been translated 2 units up and there is a horizontal asymptote at y = 2.

14. These translations lead to the following formulas for identifying asymptotes in rational functions.

15. Example 2A: Identifying Asymptotes
Identify the asymptotes.
Step 1 Write in y = form.
Step 2 Identify the asymptotes.
vertical: x = –7
horizontal: y = 0

16. Example 2B: Identifying Asymptotes
Identify the asymptotes.
Step 1 Identify the vertical asymptote.
2x – 3 = 0
Find the excluded value. Set the denominator equal to 0.
+3 +3
2x = 3
Add 3 to both sides.
Solve for x. Is an excluded value.

17. Example 2B Continued
Identify the asymptotes.
Step 2 Identify the horizontal asymptote.
c = 8
y = 8
y = c
Vertical asymptote: x = ; horizontal asymptote: y = 8

18. Check It Out! Example 2a
Identify the asymptotes.
Step 1 Identify the vertical asymptote.
x – 5 = 0
Find the excluded value. Set the denominator equal to 0.
+5 +5
x = 5
Add 5 to both sides.
x = 5
Solve for x. 5 is an excluded value.

19. Check It Out! Example 2a Continued
Identify the asymptotes.
Step 2 Identify the horizontal asymptote.
c = 0
y = 0
y = c
Vertical asymptote: x = 5; horizontal asymptote: y = 0

20. Check It Out! Example 2b
Identify the asymptotes.
Step 1 Identify the vertical asymptote.
4x + 16 = 0
Find the excluded value. Set the denominator equal to 0.
–16 –16
4x = –16
Subtract 16 from both sides.
x = –4
Solve for x. –4 is an excluded value.

21. Check It Out! Example 2b Continued
Identify the asymptotes.
Step 2 Identify the horizontal asymptote.
c = 5
y = 5
y = c
Vertical asymptote: x = –4; horizontal asymptote: y = 5

22. Check It Out! Example 2c
Identify the asymptotes.
Step 1 Identify the vertical asymptote.
x + 77 = 0
Find the excluded value. Set the denominator equal to 0.
–77 –77
x = –77
Subtract 77 from both sides.
x = –77
Solve for x. –77 is an excluded value.

23. Check It Out! Example 2c Continued
Identify the asymptotes.
Step 2 Identify the horizontal asymptote.
c = –15
y = –15
y = c
Vertical asymptote: x = –77; horizontal asymptote: y = –15

24. To graph a rational function in the form y =
when a = 1, you can graph the asymptotes and then translate the parent function y = . However, if a ≠ 1, the graph is not a translation of the parent function. In this case, you can use the asymptotes and a table of values.

25. Example 3A: Graphing Rational Functions Using Asymptotes
Graph the function.
Since the numerator is not 1, use the asymptotes and a table of values.
Step 1 Identify the vertical and horizontal asymptotes.
vertical: x = 3
Use x = b. x – 3 = 0, so b = 3.
horizontal: y = 0
Use y = c. c = 0

26. Example 3A Continued
Step 2 Graph the asymptotes using dashed lines.
Step 3 Make a table of values. Choose x-values on both sides of the vertical asymptote.
x = 3 ● y 6 5 4 2 1 x ●
y = 0
Step 4 Plot the points and connect them with smooth curves. The curves will get very close to the asymptotes, but will not touch them.

27. Example 3B: Graphing Rational Functions Using Asymptotes
Graph the function.
Step 1 Since the numerator is 1, use the asymptotes and translate y = .
vertical: x = –4
Use x = b. b = –4
horizontal: y = –2
Use y = c. c = –2

28. Example 3B Continued
Step 2 Graph the asymptotes using dashed lines.
Step 3 Draw smooth curves to show the translation.

29. Check It Out! Example 3a
Graph each function.
Step 1 Since the numerator is 1, use the asymptotes and translate y = .
vertical: x = –7
Use x = b. b = –7
horizontal: y = 3
Use y = c. c = 3

30. Check It Out! Example 3a Continued
Graph each function.
Step 2 Graph the asymptotes using dashed lines.
Step 3 Draw smooth curves to show the translation.

31. Check It Out! Example 3b
Graph each function.
Since the numerator is not 1, use the asymptotes and a table of values.
Step 1 Identify the vertical and horizontal asymptotes.
vertical: x = 3
Use x = b. x – 3 = 0, so b = 3.
horizontal: y = 2
Use y = c. c = 2

32. y 6 5 4 2 1 x Check It Out! Example 3b
Step 2 Graph the asymptotes using dashed lines.
Step 3 Make a table of values. Choose x-values on both sides of the vertical asymptote. y 6 5 4 2 1 x
Step 4 Plot the points and connect them with smooth curves. The curves will get very close to the asymptotes, but will not touch them.

33. Example 4: Application
Your club has $75 with which to purchase snacks to sell at an afterschool game. The number of snacks y that you can buy, if the average price of the snacks is x-dollars, is given by y =
a. Describe the reasonable domain and range values.
Both the number of snacks purchased and their cost will be nonnegative values so nonnegative values are reasonable for both domain and range.

34. Example 4 Continued
b. Graph the function.
Step 1 Identify the vertical and horizontal asymptotes.
vertical: x = 0
horizontal: y = 0
Use x = b. b = 0
Use y = c. c = 0
Step 2 Graph the asymptotes using dashed lines. The asymptotes will be the x- and y-axes.

35. 2 4 6 8 37.5 18.75 12.5 9.38 Example 4 Continued Number of snacks
Step 3 Since the domain is restricted to nonnegative values, only choose x-values on the right side of the vertical asymptote.
Number of snacks 2 4 6 8
Cost of snacks($)
37.5
18.75
12.5
9.38

36. Example 4 Continued
Step 4 Plot the points and connect them with a smooth curve.

37. Check It Out! Example 4
A librarian has a budget of $500 to buy copies of a software program. She will receive 10 free copies when she sets up an account with the supplier. The number of copies y of the program that she can buy is given by
y = , where x is the price per copy.
a. Describe the reasonable domain and range values.
The domain would be all values greater than 0 up to $500 dollars and the range would be all natural numbers greater than 10.

38. Check It Out! Example 4 Continued
b. Graph the function.
Step 1 Identify the vertical and horizontal asymptotes.
vertical: x = 0
horizontal: y = 10
Use x = b. b = 0
Use y = c. c = 10
Step 2 Graph the asymptotes using dashed lines. The asymptotes will be the x- and y-axes.

39. Check It Out! Example 4 Continued
Step 3 Since the domain is restricted to nonnegative values, only choose x-values on the right side of the vertical asymptote.
Number of copies 20 40 60 80
Price ($) 35 23 18 16

40. Check It Out! Example 4 Continued
Step 4 Plot the points and connect them with a smooth curve.

41. The table shows some of the properties of the four families of functions you have studied and their graphs.

44. Lesson Quiz: Part I
Identify the exceeded value for each rational function. 1. 2. 5
3. Identify the asymptotes of and then graph the function.
x = –4; y = 0

45. Lesson Quiz: Part II
You have $ 100 to spend on CDs. A CD club advertises 6 free CDs for anyone who becomes a member. The number of CDs y
that you can receive is given by y = , where x is the average price per CD.
a. Describe the reasonable domain and range values.
D: x > 0
R: natural numbers > 6

46. Lesson Quiz: Part III
b. Graph the function.