Oblique Asymptotes

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HomeAcademics & The Arts ArticlesMath ArticlesAlgebra ArticlesOblique AsymptotesByMary Jane Sterling Updated2016-03-26 10:57:21From the bookNo items found.Share
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An oblique or slant asymptote acts much like its cousins, the vertical and horizontal asymptotes. In other words, it helps you determine the ultimate direction or shape of the graph of a rational function. An oblique asymptote sometimes occurs when you have no horizontal asymptote. Oblique asymptotes take special circumstances, but the equations of these asymptotes are relatively easy to find when they do occur.

The rule for oblique asymptotes is that if the highest variable power in a rational function occurs in the numerator — and if that power is exactly one more than the highest power in the denominator — then the function has an oblique asymptote.

You can find the equation of the oblique asymptote by dividing the numerator of the function rule by the denominator and using the first two terms in the quotient in the equation of the line that is the asymptote.

Sample question

  1. Find the equation of the oblique asymptote in the function

    image0.jpg

    y=x+ 2. To find this equation, you have to divide the denominator of the function rule into the numerator. This step requires long division. You can’t use synthetic division because the divisor isn’t a binomial in the form xa. Here’s what the long division looks like:

    image1.jpg

    Ignore the remainder, and just use the first two terms in the quotient in the equation of the line.

Practice questions

  1. Find the equation of the oblique asymptote in the function

    image2.jpg
  2. Find the equation of the oblique asymptote in the function

    image3.jpg
  3. Find the equation of the oblique asymptote in the function

    image4.jpg
  4. Find the equation of the oblique asymptote in the function

    image5.jpg

Following are answers to the practice questions:

  1. The answer is y = x– 2.

    Use synthetic division or long division to divide the denominator into the numerator:

    image6.jpg

    The first two terms in the quotient are the slope and y-intercept of the oblique asymptote’s equation.

  2. The answer is y = x+ 1.

    Use synthetic division or long division to divide the denominator into the numerator:

    image7.png

    The first two terms in the quotient are the slope and y-intercept of the oblique asymptote’s equation.

  3. The answer is y = x –1.

    Use long division to divide the denominator into the numerator:

    image8.jpg

    The first two terms in the quotient are the slope and y-intercept of the oblique asymptote’s equation.

  4. The answer is y = –3x+ 13.

    Use long division to divide the denominator into the numerator:

    image9.jpg

    The first two terms in the quotient are the slope and y-intercept of the oblique asymptote’s equation.

About This Article

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About the book author:

Mary Jane Sterling (Peoria, Illinois) is the author of Algebra I For Dummies, Algebra Workbook For Dummies, Algebra II For Dummies, Algebra II Workbook For Dummies, and many other For Dummies books. She taught at Bradley University in Peoria, Illinois for more than 30 years, teaching algebra, business calculus, geometry, and finite mathematics.

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