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Math 4 graphing rational functions
1. Graphing Rational Functions1
Mathematics 4
January 3, 2012
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2. Review of Previous Concepts on Rational Functions
Rational Functions
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3. Review of Previous Concepts on Rational Functions
Rational Functions
p(x)
A rational function can be expressed as f (x) = where p(x)
q(x)
and q(x) are polynomial functions.
Mathematics 4 () Graphing Rational Functions1 January 3, 2012 2/1
4. Review of Previous Concepts on Rational Functions
Rational Functions
p(x)
A rational function can be expressed as f (x) = where p(x)
q(x)
and q(x) are polynomial functions.
The domain of f (x) is R excluding the values where the denominator
q(x) is zero.
Mathematics 4 () Graphing Rational Functions1 January 3, 2012 2/1
5. Review of Previous Concepts on Rational Functions
Rational Functions
p(x)
A rational function can be expressed as f (x) = where p(x)
q(x)
and q(x) are polynomial functions.
The domain of f (x) is R excluding the values where the denominator
q(x) is zero.
The zeros of the numerator p(x) are the zeros of the rational function
f (x).
Mathematics 4 () Graphing Rational Functions1 January 3, 2012 2/1
6. Review of Previous Concepts on Rational Functions
Rational Functions
p(x)
A rational function can be expressed as f (x) = where p(x)
q(x)
and q(x) are polynomial functions.
The domain of f (x) is R excluding the values where the denominator
q(x) is zero.
The zeros of the numerator p(x) are the zeros of the rational function
f (x).
If f (x) is in lowest terms, the zeros of the denominator q(x)
determine the vertical asymptotes of the function.
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8. The Horizontal Asymptote
Horizontal Asymptotes
The horizontal asymptote is an imaginary line that a rational
function approaches as x → −∞ and x → ∞.
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9. The Horizontal Asymptote
Horizontal Asymptotes
The horizontal asymptote is an imaginary line that a rational
function approaches as x → −∞ and x → ∞.
The graph of a rational function CAN cross its horizontal asymptotes.
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10. The Horizontal Asymptote
Consider the function below:
3x + 5
f (x) =
x−5
f (−100) =
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11. The Horizontal Asymptote
Consider the function below:
3x + 5
f (x) =
x−5
f (−100) =
Mathematics 4 () Graphing Rational Functions1 January 3, 2012 4/1
12. The Horizontal Asymptote
Consider the function below:
3x + 5
f (x) =
x−5
f (−100) = 2.809
f (−1000) =
Mathematics 4 () Graphing Rational Functions1 January 3, 2012 4/1
13. The Horizontal Asymptote
Consider the function below:
3x + 5
f (x) =
x−5
f (−100) = 2.809
f (−1000) =
Mathematics 4 () Graphing Rational Functions1 January 3, 2012 4/1
14. The Horizontal Asymptote
Consider the function below:
3x + 5
f (x) =
x−5
f (−100) = 2.809
f (−1000) = 2.98009
f (−10000) =
Mathematics 4 () Graphing Rational Functions1 January 3, 2012 4/1
15. The Horizontal Asymptote
Consider the function below:
3x + 5
f (x) =
x−5
f (−100) = 2.809
f (−1000) = 2.98009
f (−10000) =
Mathematics 4 () Graphing Rational Functions1 January 3, 2012 4/1
16. The Horizontal Asymptote
Consider the function below:
3x + 5
f (x) =
x−5
f (−100) = 2.809 f (100) =
f (−1000) = 2.98009
f (−10000) = 2.998
Mathematics 4 () Graphing Rational Functions1 January 3, 2012 4/1
17. The Horizontal Asymptote
Consider the function below:
3x + 5
f (x) =
x−5
f (−100) = 2.809 f (100) =
f (−1000) = 2.98009
f (−10000) = 2.998
Mathematics 4 () Graphing Rational Functions1 January 3, 2012 4/1
18. The Horizontal Asymptote
Consider the function below:
3x + 5
f (x) =
x−5
f (−100) = 2.809 f (100) = 3.2105
f (−1000) = 2.98009 f (1000) =
f (−10000) = 2.998
Mathematics 4 () Graphing Rational Functions1 January 3, 2012 4/1
19. The Horizontal Asymptote
Consider the function below:
3x + 5
f (x) =
x−5
f (−100) = 2.809 f (100) = 3.2105
f (−1000) = 2.98009 f (1000) =
f (−10000) = 2.998
Mathematics 4 () Graphing Rational Functions1 January 3, 2012 4/1
20. The Horizontal Asymptote
Consider the function below:
3x + 5
f (x) =
x−5
f (−100) = 2.809 f (100) = 3.2105
f (−1000) = 2.98009 f (1000) = 3.0201
f (−10000) = 2.998 f (10000) =
Mathematics 4 () Graphing Rational Functions1 January 3, 2012 4/1
21. The Horizontal Asymptote
Consider the function below:
3x + 5
f (x) =
x−5
f (−100) = 2.809 f (100) = 3.2105
f (−1000) = 2.98009 f (1000) = 3.0201
f (−10000) = 2.998 f (10000) =
Mathematics 4 () Graphing Rational Functions1 January 3, 2012 4/1
22. The Horizontal Asymptote
Consider the function below:
3x + 5
f (x) =
x−5
f (−100) = 2.809 f (100) = 3.2105
f (−1000) = 2.98009 f (1000) = 3.0201
f (−10000) = 2.998 f (10000) = 3.002
Mathematics 4 () Graphing Rational Functions1 January 3, 2012 4/1
23. The Horizontal Asymptote
Consider the function below:
3x + 5
f (x) =
x−5
f (−100) = 2.809 f (100) = 3.2105
f (−1000) = 2.98009 f (1000) = 3.0201
f (−10000) = 2.998 f (10000) = 3.002
As x → −∞ and as x → ∞, the value of f (x) becomes closer to 3.
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24. The Horizontal Asymptote
Consider the function below:
3x + 5
f (x) =
x−5
f (−100) = 2.809 f (100) = 3.2105
f (−1000) = 2.98009 f (1000) = 3.0201
f (−10000) = 2.998 f (10000) = 3.002
As x → −∞ and as x → ∞, the value of f (x) becomes closer to 3.
The horizontal asymptote is the line y = 3.
Mathematics 4 () Graphing Rational Functions1 January 3, 2012 4/1
25. The Horizontal Asymptote
3x3 + 4x2 + 7x + 2
Consider the function f (x) =
4x3 − 5x2 + 3x + 1
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26. The Horizontal Asymptote
3x3 + 4x2 + 7x + 2
Consider the function f (x) =
4x3 − 5x2 + 3x + 1
Let’s analyze the function as x → −∞: (please refer to the blackboard)
Mathematics 4 () Graphing Rational Functions1 January 3, 2012 5/1
27. The Horizontal Asymptote
3x3 + 4x2 + 7x + 2
Consider the function f (x) =
4x3 − 5x2 + 3x + 1
Let’s analyze the function as x → −∞: (please refer to the blackboard)
Now analyze the function as x → ∞: (please refer to the blackboard)
Mathematics 4 () Graphing Rational Functions1 January 3, 2012 5/1
28. The Horizontal Asymptote
3x3 + 4x2 + 7x + 2
Consider the function f (x) =
4x3 − 5x2 + 3x + 1
Let’s analyze the function as x → −∞: (please refer to the blackboard)
Now analyze the function as x → ∞: (please refer to the blackboard)
The horizontal asymptote is y = 3 .
4
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29. The Horizontal Asymptote
degree of p(x) = degree of q(x)
If the degree of the numerator p(x) is equal to the degree of the
denominator q(x), the horizontal asymptote is
an
y=
bn
where an is the leading coefficient of p(x) and q(x) is the leading
coefficient of q(x).
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30. The Horizontal Asymptote
5x + 2
Consider the function f (x) =
3x3 − x2 − 8x − 2
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31. The Horizontal Asymptote
5x + 2
Consider the function f (x) =
3x3 − x2 − 8x − 2
Let’s analyze the function as x → −∞: (please refer to the blackboard)
Mathematics 4 () Graphing Rational Functions1 January 3, 2012 7/1
32. The Horizontal Asymptote
5x + 2
Consider the function f (x) =
3x3 − x2 − 8x − 2
Let’s analyze the function as x → −∞: (please refer to the blackboard)
Now analyze the function as x → ∞: (please refer to the blackboard)
Mathematics 4 () Graphing Rational Functions1 January 3, 2012 7/1
33. The Horizontal Asymptote
5x + 2
Consider the function f (x) =
3x3 − x2 − 8x − 2
Let’s analyze the function as x → −∞: (please refer to the blackboard)
Now analyze the function as x → ∞: (please refer to the blackboard)
The horizontal asymptote is y = 0.
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34. The Horizontal Asymptote
degree of p(x) < degree of q(x)
If the degree of the numerator p(x) is less than the degree of the
denominator q(x), the horizontal asymptote is
y=0
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35. The Horizontal Asymptote
Summary
an xn + ... + a1 x + a0
The graph of f (x) = has:
bm xm + ... + b1 x + b0
its HA at the x-axis n<m
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36. The Horizontal Asymptote
Summary
an xn + ... + a1 x + a0
The graph of f (x) = has:
bm xm + ... + b1 x + b0
its HA at the x-axis n<m
Mathematics 4 () Graphing Rational Functions1 January 3, 2012 9/1
37. The Horizontal Asymptote
Summary
an xn + ... + a1 x + a0
The graph of f (x) = has:
bm xm + ... + b1 x + b0
its HA at the x-axis n<m
an
its HA at y = n=m
bm
Mathematics 4 () Graphing Rational Functions1 January 3, 2012 9/1
38. The Horizontal Asymptote
Summary
an xn + ... + a1 x + a0
The graph of f (x) = has:
bm xm + ... + b1 x + b0
its HA at the x-axis n<m
an
its HA at y = n=m
bm
no horizontal asymptote n>m
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39. Graphing Rational Functions
Graphing
The following information is needed to graph a rational function f (x):
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40. Graphing Rational Functions
Graphing
The following information is needed to graph a rational function f (x):
1 Domain of f (x)
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41. Graphing Rational Functions
Graphing
The following information is needed to graph a rational function f (x):
1 Domain of f (x)
2 Zeros of f (x)
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42. Graphing Rational Functions
Graphing
The following information is needed to graph a rational function f (x):
1 Domain of f (x)
2 Zeros of f (x)
3 The vertical asymptotes (if any)
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43. Graphing Rational Functions
Graphing
The following information is needed to graph a rational function f (x):
1 Domain of f (x)
2 Zeros of f (x)
3 The vertical asymptotes (if any)
4 The horizontal asymptote (if any)
Mathematics 4 () Graphing Rational Functions1 January 3, 2012 10 / 1
44. Graphing Rational Functions
Graphing
The following information is needed to graph a rational function f (x):
1 Domain of f (x)
2 Zeros of f (x)
3 The vertical asymptotes (if any)
4 The horizontal asymptote (if any)
5 The y-intercept
Mathematics 4 () Graphing Rational Functions1 January 3, 2012 10 / 1
45. Graphing Rational Functions
Graphing
The following information is needed to graph a rational function f (x):
1 Domain of f (x)
2 Zeros of f (x)
3 The vertical asymptotes (if any)
4 The horizontal asymptote (if any)
5 The y-intercept
6 The table of signs
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82. Assignment: Homework 12 due tomorrow.
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83. Graphing Rational Functions with Oblique Asymptotes
Oblique Asymptote
n
A rational function f (x) = bmx m+...+a11x+a0 has an oblique asymptote if it
an
x +...+b x+b0
is in lowest terms and n = m + 1.
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84. Graphing Rational Functions with Oblique Asymptotes
Oblique Asymptote
n
A rational function f (x) = bmx m+...+a11x+a0 has an oblique asymptote if it
an
x +...+b x+b0
is in lowest terms and n = m + 1.
Functions with oblique asymptotes
x2 − 2x + 1
f (x) =
x
x 2 + 6x + 8
f (x) =
x+3
x3 + 7x2 − 20x − 96
f (x) =
x2 − 10x + 16
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85. Graphing Rational Functions with Oblique Asymptotes
Oblique Asymptote
The oblique asymptote is a line of the form y = mx + b.
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86. Graphing Rational Functions with Oblique Asymptotes
Oblique Asymptote
The oblique asymptote is a line of the form y = mx + b.
Finding the oblique asymptote
Take the polynomial part of the long division of the rational function.
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87. Graphing Rational Functions with Oblique Asymptotes
Oblique Asymptote
x2 −2x+1
Find the oblique asymptote of f (x) = x :
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88. Graphing Rational Functions with Oblique Asymptotes
Oblique Asymptote
x2 −2x+1
Find the oblique asymptote of f (x) = x :
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89. Graphing Rational Functions with Oblique Asymptotes
Oblique Asymptote
x2 −2x+1
Find the oblique asymptote of f (x) = x :
x−2
x x2 − 2x + 1
− x2
− 2x
2x
The oblique asymptote is y = x − 2.
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90. Graphing Rational Functions with Oblique Asymptotes
Oblique Asymptote
x2 +6x+8
Find the oblique asymptote of f (x) = x+3 :
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91. Graphing Rational Functions with Oblique Asymptotes
Oblique Asymptote
x2 +6x+8
Find the oblique asymptote of f (x) = x+3 :
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92. Graphing Rational Functions with Oblique Asymptotes
Oblique Asymptote
x2 +6x+8
Find the oblique asymptote of f (x) = x+3 :
x+3
x+3 x2+ 6x + 8
− x2 − 3x
3x + 8
− 3x − 9
−1
The oblique asymptote is y = x + 3.
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93. Graphing Rational Functions with Oblique Asymptotes
Oblique Asymptote
x3 +7x2 −20x−96
Find the oblique asymptote of f (x) = x2 −10x+16
:
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94. Graphing Rational Functions with Oblique Asymptotes
Oblique Asymptote
x3 +7x2 −20x−96
Find the oblique asymptote of f (x) = x2 −10x+16
:
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95. Graphing Rational Functions with Oblique Asymptotes
Oblique Asymptote
x3 +7x2 −20x−96
Find the oblique asymptote of f (x) = x2 −10x+16
:
x + 17
x2 − 10x + 16 x3+ 7x2
− 20x − 96
− x3 + 10x2 − 16x
17x2 − 36x − 96
− 17x2 + 170x − 272
134x − 368
The oblique asymptote is y = x + 17.
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96. Graphing Rational Functions with Oblique Asymptotes
Oblique Asymptote
3x3 −2x2 +4x−3
Find the oblique asymptote of f (x) = x2 +3x+3
:
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97. Graphing Rational Functions with Oblique Asymptotes
Oblique Asymptote
3x3 −2x2 +4x−3
Find the oblique asymptote of f (x) = x2 +3x+3
:
Mathematics 4 () Graphing Rational Functions1 January 3, 2012 45 / 1
98. Graphing Rational Functions with Oblique Asymptotes
Oblique Asymptote
3x3 −2x2 +4x−3
Find the oblique asymptote of f (x) = x2 +3x+3
:
3x − 11
x2 + 3x + 3 3x3
− 2x2
+ 4x − 3
− 3x3 − 9x2 − 9x
− 11x2 − 5x − 3
11x2 + 33x + 33
28x + 30
The oblique asymptote is y = 3x − 11.
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99. Graphing Rational Functions with Oblique Asymptotes
x2 +6x+8
Example: f (x) = x+3
y
4
3
2
1
x
−7 −6 −5 −4 −3 −2 −1 1 2
−1
−2
−3
−4
Domain:
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100. Graphing Rational Functions with Oblique Asymptotes
x2 +6x+8
Example: f (x) = x+3
y
4
3
2
1
x
−7 −6 −5 −4 −3 −2 −1 1 2
−1
−2
−3
−4
Domain:
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101. Graphing Rational Functions with Oblique Asymptotes
x2 +6x+8
Example: f (x) = x+3
y
4
3
2
1
x
−7 −6 −5 −4 −3 −2 −1 1 2
−1
−2
−3
−4
Domain: x = −3
Mathematics 4 () Graphing Rational Functions1 January 3, 2012 46 / 1
102. Graphing Rational Functions with Oblique Asymptotes
x2 +6x+8
Example: f (x) = x+3
y
4
3
2
1
x
−7 −6 −5 −4 −3 −2 −1 1 2
−1
−2
−3
−4
Zeros:
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103. Graphing Rational Functions with Oblique Asymptotes
x2 +6x+8
Example: f (x) = x+3
y
4
3
2
1
x
−7 −6 −5 −4 −3 −2 −1 1 2
−1
−2
−3
−4
Zeros: −4, −2
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104. Graphing Rational Functions with Oblique Asymptotes
x2 +6x+8
Example: f (x) = x+3
y
4
3
2
1
x
−7 −6 −5 −4 −3 −2 −1 1 2
−1
−2
−3
−4
y-intercept:
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105. Graphing Rational Functions with Oblique Asymptotes
x2 +6x+8
Example: f (x) = x+3
y
4
3
2
1
x
−7 −6 −5 −4 −3 −2 −1 1 2
−1
−2
−3
−4
8
y-intercept: 3
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106. Graphing Rational Functions with Oblique Asymptotes
x2 +6x+8
Example: f (x) = x+3
y
4
3
2
1
x
−7 −6 −5 −4 −3 −2 −1 1 2
−1
−2
−3
−4
vertical asymptotes:
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107. Graphing Rational Functions with Oblique Asymptotes
x2 +6x+8
Example: f (x) = x+3
y
4
3
2
1
x
−7 −6 −5 −4 −3 −2 −1 1 2
−1
−2
−3
−4
vertical asymptotes: x = −3
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108. Graphing Rational Functions with Oblique Asymptotes
x2 +6x+8
Example: f (x) = x+3
y
4
3
2
1
x
−7 −6 −5 −4 −3 −2 −1 1 2
−1
−2
−3
−4
oblique asymptote:
Mathematics 4 () Graphing Rational Functions1 January 3, 2012 53 / 1
109. Graphing Rational Functions with Oblique Asymptotes
x2 +6x+8
Example: f (x) = x+3
y
4
3
2
1
x
−7 −6 −5 −4 −3 −2 −1 1 2
−1
−2
−3
−4
oblique asymptote: y =x+3
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