Precalculus Examples

Find the Asymptotes f(x)=(x^3)/(x^2-9)
Step 1
Find where the expression is undefined.
Step 2
Since as from the left and as from the right, then is a vertical asymptote.
Step 3
Since as from the left and as from the right, then is a vertical asymptote.
Step 4
List all of the vertical asymptotes:
Step 5
Consider the rational function where is the degree of the numerator and is the degree of the denominator.
1. If , then the x-axis, , is the horizontal asymptote.
2. If , then the horizontal asymptote is the line .
3. If , then there is no horizontal asymptote (there is an oblique asymptote).
Step 6
Find and .
Step 7
Since , there is no horizontal asymptote.
No Horizontal Asymptotes
Step 8
Find the oblique asymptote using polynomial division.
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Step 8.1
Simplify the denominator.
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Step 8.1.1
Rewrite as .
Step 8.1.2
Since both terms are perfect squares, factor using the difference of squares formula, where and .
Step 8.2
Expand .
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Step 8.2.1
Apply the distributive property.
Step 8.2.2
Apply the distributive property.
Step 8.2.3
Apply the distributive property.
Step 8.2.4
Reorder and .
Step 8.2.5
Raise to the power of .
Step 8.2.6
Raise to the power of .
Step 8.2.7
Use the power rule to combine exponents.
Step 8.2.8
Add and .
Step 8.2.9
Multiply by .
Step 8.2.10
Add and .
Step 8.2.11
Subtract from .
Step 8.3
Set up the polynomials to be divided. If there is not a term for every exponent, insert one with a value of .
+-+++
Step 8.4
Divide the highest order term in the dividend by the highest order term in divisor .
+-+++
Step 8.5
Multiply the new quotient term by the divisor.
+-+++
++-
Step 8.6
The expression needs to be subtracted from the dividend, so change all the signs in
+-+++
--+
Step 8.7
After changing the signs, add the last dividend from the multiplied polynomial to find the new dividend.
+-+++
--+
+
Step 8.8
Pull the next term from the original dividend down into the current dividend.
+-+++
--+
++
Step 8.9
The final answer is the quotient plus the remainder over the divisor.
Step 8.10
The oblique asymptote is the polynomial portion of the long division result.
Step 9
This is the set of all asymptotes.
Vertical Asymptotes:
No Horizontal Asymptotes
Oblique Asymptotes:
Step 10