Precalculus Examples

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

Step 1

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

$x = - 3, x = - 2, x = 1, x = 2$

Step 2

Since $\frac{(x - 1) {(x - 3)}^{2} {(x + 1)}^{2}}{(x - 2) (x + 2) (x - 1) (x + 3)}$ $\to$ $- \infty$ as $x$ $\to$ $- 3$ from the left and $\frac{(x - 1) {(x - 3)}^{2} {(x + 1)}^{2}}{(x - 2) (x + 2) (x - 1) (x + 3)}$ $\to$ $\infty$ as $x$ $\to$ $- 3$ from the right, then $x = - 3$ is a vertical asymptote.

$x = - 3$

Step 3

Since $\frac{(x - 1) {(x - 3)}^{2} {(x + 1)}^{2}}{(x - 2) (x + 2) (x - 1) (x + 3)}$ $\to$ $\infty$ as $x$ $\to$ $- 2$ from the left and $\frac{(x - 1) {(x - 3)}^{2} {(x + 1)}^{2}}{(x - 2) (x + 2) (x - 1) (x + 3)}$ $\to$ $- \infty$ as $x$ $\to$ $- 2$ from the right, then $x = - 2$ is a vertical asymptote.

$x = - 2$

Step 4

Since $\frac{(x - 1) {(x - 3)}^{2} {(x + 1)}^{2}}{(x - 2) (x + 2) (x - 1) (x + 3)}$ $\to$ $- \infty$ as $x$ $\to$ $2$ from the left and $\frac{(x - 1) {(x - 3)}^{2} {(x + 1)}^{2}}{(x - 2) (x + 2) (x - 1) (x + 3)}$ $\to$ $\infty$ as $x$ $\to$ $2$ from the right, then $x = 2$ is a vertical asymptote.

$x = 2$

Step 5

List all of the vertical asymptotes:

$x = - 3, - 2, 2$

Step 6

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 7

Find $n$ and $m$ .

$n = 5$

$m = 4$

Step 8

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

No Horizontal Asymptotes

Step 9

Find the oblique asymptote using polynomial division.

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Step 9.1

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

$x^{4}$

$2 x^{3}$

$7 x^{2}$

$8 x$

$12$

$x^{5}$

$5 x^{4}$

$2 x^{3}$

$14 x^{2}$

$3 x$

$9$

Step 9.2

Divide the highest order term in the dividend $x^{5}$ by the highest order term in divisor $x^{4}$ .

$x$

$x^{4}$

$2 x^{3}$

$7 x^{2}$

$8 x$

$12$

$x^{5}$

$5 x^{4}$

$2 x^{3}$

$14 x^{2}$

$3 x$

$9$

Step 9.3

Multiply the new quotient term by the divisor.

$x$

$x^{4}$

$2 x^{3}$

$7 x^{2}$

$8 x$

$12$

$x^{5}$

$5 x^{4}$

$2 x^{3}$

$14 x^{2}$

$3 x$

$9$

$x^{5}$

$2 x^{4}$

$7 x^{3}$

$8 x^{2}$

$12 x$

Step 9.4

The expression needs to be subtracted from the dividend, so change all the signs in $x^{5} + 2 x^{4} - 7 x^{3} - 8 x^{2} + 12 x$

$x$

$x^{4}$

$2 x^{3}$

$7 x^{2}$

$8 x$

$12$

$x^{5}$

$5 x^{4}$

$2 x^{3}$

$14 x^{2}$

$3 x$

$9$

$x^{5}$

$2 x^{4}$

$7 x^{3}$

$8 x^{2}$

$12 x$

Step 9.5

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

$x$

$x^{4}$

$2 x^{3}$

$7 x^{2}$

$8 x$

$12$

$x^{5}$

$5 x^{4}$

$2 x^{3}$

$14 x^{2}$

$3 x$

$9$

$x^{5}$

$2 x^{4}$

$7 x^{3}$

$8 x^{2}$

$12 x$

$7 x^{4}$

$9 x^{3}$

$22 x^{2}$

$15 x$

Step 9.6

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

$x$

$x^{4}$

$2 x^{3}$

$7 x^{2}$

$8 x$

$12$

$x^{5}$

$5 x^{4}$

$2 x^{3}$

$14 x^{2}$

$3 x$

$9$

$x^{5}$

$2 x^{4}$

$7 x^{3}$

$8 x^{2}$

$12 x$

$7 x^{4}$

$9 x^{3}$

$22 x^{2}$

$15 x$

$9$

Step 9.7

Divide the highest order term in the dividend $- 7 x^{4}$ by the highest order term in divisor $x^{4}$ .

$x$

$7$

$x^{4}$

$2 x^{3}$

$7 x^{2}$

$8 x$

$12$

$x^{5}$

$5 x^{4}$

$2 x^{3}$

$14 x^{2}$

$3 x$

$9$

$x^{5}$

$2 x^{4}$

$7 x^{3}$

$8 x^{2}$

$12 x$

$7 x^{4}$

$9 x^{3}$

$22 x^{2}$

$15 x$

$9$

Step 9.8

Multiply the new quotient term by the divisor.

$x$

$7$

$x^{4}$

$2 x^{3}$

$7 x^{2}$

$8 x$

$12$

$x^{5}$

$5 x^{4}$

$2 x^{3}$

$14 x^{2}$

$3 x$

$9$

$x^{5}$

$2 x^{4}$

$7 x^{3}$

$8 x^{2}$

$12 x$

$7 x^{4}$

$9 x^{3}$

$22 x^{2}$

$15 x$

$9$

$7 x^{4}$

$14 x^{3}$

$49 x^{2}$

$56 x$

$84$

Step 9.9

The expression needs to be subtracted from the dividend, so change all the signs in $- 7 x^{4} - 14 x^{3} + 49 x^{2} + 56 x - 84$

$x$

$7$

$x^{4}$

$2 x^{3}$

$7 x^{2}$

$8 x$

$12$

$x^{5}$

$5 x^{4}$

$2 x^{3}$

$14 x^{2}$

$3 x$

$9$

$x^{5}$

$2 x^{4}$

$7 x^{3}$

$8 x^{2}$

$12 x$

$7 x^{4}$

$9 x^{3}$

$22 x^{2}$

$15 x$

$9$

$7 x^{4}$

$14 x^{3}$

$49 x^{2}$

$56 x$

$84$

Step 9.10

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

$x$

$7$

$x^{4}$

$2 x^{3}$

$7 x^{2}$

$8 x$

$12$

$x^{5}$

$5 x^{4}$

$2 x^{3}$

$14 x^{2}$

$3 x$

$9$

$x^{5}$

$2 x^{4}$

$7 x^{3}$

$8 x^{2}$

$12 x$

$7 x^{4}$

$9 x^{3}$

$22 x^{2}$

$15 x$

$9$

$7 x^{4}$

$14 x^{3}$

$49 x^{2}$

$56 x$

$84$

$23 x^{3}$

$27 x^{2}$

$71 x$

$75$

Step 9.11

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

$x - 7 + \frac{23 x^{3} - 27 x^{2} - 71 x + 75}{x^{4} + 2 x^{3} - 7 x^{2} - 8 x + 12}$

Step 9.12

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

$y = x - 7$

Step 10

This is the set of all asymptotes.

Vertical Asymptotes: $x = - 3, - 2, 2$

No Horizontal Asymptotes

Oblique Asymptotes: $y = x - 7$

Step 11