Precalculus Examples

$f (x) = \frac{x^{2} + 1}{3 (x - 8)}$

Step 1

Find where the expression $\frac{x^{2} + 1}{3 (x - 8)}$ is undefined.

$x = 8$

Step 2

Consider the rational function $R (x) = \frac{a x^{n}}{b x^{m}}$ where $n$ is the degree of the numerator and $m$ is the degree of the denominator.

1. If $n < m$ , then the x-axis, $y = 0$ , is the horizontal asymptote.

2. If $n = m$ , then the horizontal asymptote is the line $y = \frac{a}{b}$ .

3. If $n > m$ , then there is no horizontal asymptote (there is an oblique asymptote).

Step 3

Find $n$ and $m$ .

$n = 2$

$m = 1$

Step 4

Since $n > m$ , there is no horizontal asymptote.

No Horizontal Asymptotes

Step 5

Find the oblique asymptote using polynomial division.

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Step 5.1

Factor $3$ out of $3 x - 24$ .

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Step 5.1.1

Factor $3$ out of $3 x$ .

$\frac{x^{2} + 1}{3 (x) - 24}$

Step 5.1.2

Factor $3$ out of $- 24$ .

$\frac{x^{2} + 1}{3 x + 3 \cdot - 8}$

Step 5.1.3

Factor $3$ out of $3 x + 3 \cdot - 8$ .

$\frac{x^{2} + 1}{3 (x - 8)}$

Step 5.2

Expand $3 (x - 8)$ .

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Step 5.2.1

Apply the distributive property.

$\frac{x^{2} + 1}{3 x + 3 \cdot - 8}$

Step 5.2.2

Multiply $3$ by $- 8$ .

$\frac{x^{2} + 1}{3 x - 24}$

Step 5.3

Set up the polynomials to be divided. If there is not a term for every exponent, insert one with a value of $0$ .

$3 x$

$24$

$x^{2}$

$0 x$

$1$

Step 5.4

Divide the highest order term in the dividend $x^{2}$ by the highest order term in divisor $3 x$ .

					$\frac{x}{3}$
	$3 x$	-	$24$		$x^{2}$	+	$0 x$	+	$1$

Step 5.5

Multiply the new quotient term by the divisor.

				$\frac{x}{3}$
$3 x$	-	$24$		$x^{2}$	+	$0 x$	+	$1$
			+	$x^{2}$	-	$8 x$

Step 5.6

The expression needs to be subtracted from the dividend, so change all the signs in $x^{2} - 8 x$

				$\frac{x}{3}$
$3 x$	-	$24$		$x^{2}$	+	$0 x$	+	$1$
			-	$x^{2}$	+	$8 x$

Step 5.7

After changing the signs, add the last dividend from the multiplied polynomial to find the new dividend.

				$\frac{x}{3}$
$3 x$	-	$24$		$x^{2}$	+	$0 x$	+	$1$
			-	$x^{2}$	+	$8 x$
					+	$8 x$

Step 5.8

Pull the next terms from the original dividend down into the current dividend.

				$\frac{x}{3}$
$3 x$	-	$24$		$x^{2}$	+	$0 x$	+	$1$
			-	$x^{2}$	+	$8 x$
					+	$8 x$	+	$1$

Step 5.9

Divide the highest order term in the dividend $8 x$ by the highest order term in divisor $3 x$ .

				$\frac{x}{3}$	+	$\frac{8}{3}$
$3 x$	-	$24$		$x^{2}$	+	$0 x$	+	$1$
			-	$x^{2}$	+	$8 x$
					+	$8 x$	+	$1$

Step 5.10

Multiply the new quotient term by the divisor.

				$\frac{x}{3}$	+	$\frac{8}{3}$
$3 x$	-	$24$		$x^{2}$	+	$0 x$	+	$1$
			-	$x^{2}$	+	$8 x$
					+	$8 x$	+	$1$
					+	$8 x$	-	$64$

Step 5.11

The expression needs to be subtracted from the dividend, so change all the signs in $8 x - 64$

				$\frac{x}{3}$	+	$\frac{8}{3}$
$3 x$	-	$24$		$x^{2}$	+	$0 x$	+	$1$
			-	$x^{2}$	+	$8 x$
					+	$8 x$	+	$1$
					-	$8 x$	+	$64$

Step 5.12

After changing the signs, add the last dividend from the multiplied polynomial to find the new dividend.

				$\frac{x}{3}$	+	$\frac{8}{3}$
$3 x$	-	$24$		$x^{2}$	+	$0 x$	+	$1$
			-	$x^{2}$	+	$8 x$
					+	$8 x$	+	$1$
					-	$8 x$	+	$64$
							+	$65$

Step 5.13

The final answer is the quotient plus the remainder over the divisor.

$\frac{x}{3} + \frac{8}{3} + \frac{65}{3 x - 24}$

Step 5.14

The oblique asymptote is the polynomial portion of the long division result.

$y = \frac{x}{3} + \frac{8}{3}$

Step 6

This is the set of all asymptotes.

Vertical Asymptotes: $x = 8$

No Horizontal Asymptotes

Oblique Asymptotes: $y = \frac{x}{3} + \frac{8}{3}$

Step 7