How do you find slant asymptotes?

Understand the Problem

The question is asking how to determine the slant (or oblique) asymptotes of a rational function. This involves analyzing the degrees of the polynomial in the numerator and the denominator and applying polynomial long division if the degree of the numerator is exactly one more than that of the denominator.

Answer

y = x + 2
Answer for screen readers

The final answer is y = x + 2

Steps to Solve

  1. Identify the degrees of the polynomials

Check the degree of the numerator and the degree of the denominator of your rational function. Slant asymptotes occur if the degree of the numerator is exactly one more than the degree of the denominator.

  1. Perform polynomial long division

Divide the numerator by the denominator using polynomial long division or synthetic division if applicable. The result will be a linear expression plus a remainder.

  1. Extract the linear term

The quotient from the polynomial division gives the equation of the slant asymptote. Ignore the remainder term as it becomes insignificant as x approaches infinity.

Example

For the rational function, let’s say ( \frac{x^2 + 3x + 5}{x + 1} ):

  • The degree of the numerator ((x^2)) is 2.
  • The degree of the denominator ((x)) is 1.
  • Since 2 = 1 + 1, we can proceed with the division.
  1. Setup the division

Divide (x^2 + 3x + 5) by (x + 1):

$$ x^2 \div x = x $$

  1. Multiply & subtract

Multiply (x) by (x + 1):

$$ x \cdot (x + 1) = x^2 + x $$

Subtract (x^2 + x) from (x^2 + 3x + 5):

$$ (x^2 + 3x + 5) - (x^2 + x) = 2x + 5 $$

  1. Divide again

Divide (2x) by (x):

$$ 2x \div x = 2 $$

Multiply & subtract again:

$$ 2 \cdot (x + 1) = 2x + 2 $$

Subtract (2x + 2) from (2x + 5):

$$ (2x + 5) - (2x + 2) = 3 $$

  1. Form the slant asymptote equation

The quotient of the division is (x + 2). Therefore, the slant asymptote is:

$$ y = x + 2 $$

The final answer is y = x + 2

More Information

Slant asymptotes are found in rational functions where the degree of the numerator is one more than the degree of the denominator. They show the behavior of the function at infinity.

Tips

A common mistake is failing to correctly perform the polynomial long division, particularly in keeping track of the signs and coefficients. Double-check your work to ensure accuracy.

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