Precalculus Examples

$f (x) = \frac{6 x^{5} - 4 x^{2} + 5}{6 x^{2} + 5 x - 4}$

Step 1

Find where the expression $\frac{6 x^{5} - 4 x^{2} + 5}{6 x^{2} + 5 x - 4}$ is undefined.

$x = - \frac{4}{3}, x = \frac{1}{2}$

Step 2

Since $\frac{6 x^{5} - 4 x^{2} + 5}{6 x^{2} + 5 x - 4}$ $\to$ $- \infty$ as $x$ $\to$ $- \frac{4}{3}$ from the left and $\frac{6 x^{5} - 4 x^{2} + 5}{6 x^{2} + 5 x - 4}$ $\to$ $\infty$ as $x$ $\to$ $- \frac{4}{3}$ from the right, then $x = - \frac{4}{3}$ is a vertical asymptote.

$x = - \frac{4}{3}$

Step 3

Since $\frac{6 x^{5} - 4 x^{2} + 5}{6 x^{2} + 5 x - 4}$ $\to$ $- \infty$ as $x$ $\to$ $\frac{1}{2}$ from the left and $\frac{6 x^{5} - 4 x^{2} + 5}{6 x^{2} + 5 x - 4}$ $\to$ $\infty$ as $x$ $\to$ $\frac{1}{2}$ from the right, then $x = \frac{1}{2}$ is a vertical asymptote.

$x = \frac{1}{2}$

Step 4

List all of the vertical asymptotes:

$x = - \frac{4}{3}, \frac{1}{2}$

Step 5

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 6

Find $n$ and $m$ .

$n = 5$

$m = 2$

Step 7

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

No Horizontal Asymptotes

Step 8

Find the oblique asymptote using polynomial division.

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Step 8.1

Factor by grouping.

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Step 8.1.1

For a polynomial of the form $a x^{2} + b x + c$ , rewrite the middle term as a sum of two terms whose product is $a \cdot c = 6 \cdot - 4 = - 24$ and whose sum is $b = 5$ .

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Step 8.1.1.1

Factor $5$ out of $5 x$ .

$\frac{6 x^{5} - 4 x^{2} + 5}{6 x^{2} + 5 (x) - 4}$

Step 8.1.1.2

Rewrite $5$ as $- 3$ plus $8$

$\frac{6 x^{5} - 4 x^{2} + 5}{6 x^{2} + (- 3 + 8) x - 4}$

Step 8.1.1.3

Apply the distributive property.

$\frac{6 x^{5} - 4 x^{2} + 5}{6 x^{2} - 3 x + 8 x - 4}$

Step 8.1.2

Factor out the greatest common factor from each group.

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Step 8.1.2.1

Group the first two terms and the last two terms.

$\frac{6 x^{5} - 4 x^{2} + 5}{(6 x^{2} - 3 x) + 8 x - 4}$

Step 8.1.2.2

Factor out the greatest common factor (GCF) from each group.

$\frac{6 x^{5} - 4 x^{2} + 5}{3 x (2 x - 1) + 4 (2 x - 1)}$

Step 8.1.3

Factor the polynomial by factoring out the greatest common factor, $2 x - 1$ .

$\frac{6 x^{5} - 4 x^{2} + 5}{(2 x - 1) (3 x + 4)}$

Step 8.2

Expand $(2 x - 1) (3 x + 4)$ .

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Step 8.2.1

Apply the distributive property.

$\frac{6 x^{5} - 4 x^{2} + 5}{2 x (3 x + 4) - 1 (3 x + 4)}$

Step 8.2.2

Apply the distributive property.

$\frac{6 x^{5} - 4 x^{2} + 5}{2 x (3 x) + 2 x \cdot 4 - 1 (3 x + 4)}$

Step 8.2.3

Apply the distributive property.

$\frac{6 x^{5} - 4 x^{2} + 5}{2 x (3 x) + 2 x \cdot 4 - 1 (3 x) - 1 \cdot 4}$

Step 8.2.4

Remove parentheses.

$\frac{6 x^{5} - 4 x^{2} + 5}{2 x \cdot (3 x) + 2 x \cdot 4 - 1 (3 x) - 1 \cdot 4}$

Step 8.2.5

Move $x$ .

$\frac{6 x^{5} - 4 x^{2} + 5}{2 \cdot (3 x \cdot x) + 2 x \cdot 4 - 1 (3 x) - 1 \cdot 4}$

Step 8.2.6

Move $x$ .

$\frac{6 x^{5} - 4 x^{2} + 5}{2 \cdot (3 x \cdot x) + 2 \cdot (4 x) - 1 (3 x) - 1 \cdot 4}$

Step 8.2.7

Remove parentheses.

$\frac{6 x^{5} - 4 x^{2} + 5}{2 \cdot (3 x \cdot x) + 2 \cdot (4 x) - 1 \cdot (3 x) - 1 \cdot 4}$

Step 8.2.8

Multiply $2$ by $3$ .

$\frac{6 x^{5} - 4 x^{2} + 5}{6 x \cdot x + 2 \cdot (4 x) - 1 \cdot (3 x) - 1 \cdot 4}$

Step 8.2.9

Raise $x$ to the power of $1$ .

$\frac{6 x^{5} - 4 x^{2} + 5}{6 (x \cdot x) + 2 \cdot (4 x) - 1 \cdot (3 x) - 1 \cdot 4}$

Step 8.2.10

Raise $x$ to the power of $1$ .

$\frac{6 x^{5} - 4 x^{2} + 5}{6 (x \cdot x) + 2 \cdot (4 x) - 1 \cdot (3 x) - 1 \cdot 4}$

Step 8.2.11

Use the power rule $a^{m} a^{n} = a^{m + n}$ to combine exponents.

$\frac{6 x^{5} - 4 x^{2} + 5}{6 x^{1 + 1} + 2 \cdot (4 x) - 1 \cdot (3 x) - 1 \cdot 4}$

Step 8.2.12

Add $1$ and $1$ .

$\frac{6 x^{5} - 4 x^{2} + 5}{6 x^{2} + 2 \cdot (4 x) - 1 \cdot (3 x) - 1 \cdot 4}$

Step 8.2.13

Multiply $2$ by $4$ .

$\frac{6 x^{5} - 4 x^{2} + 5}{6 x^{2} + 8 x - 1 \cdot (3 x) - 1 \cdot 4}$

Step 8.2.14

Multiply $- 1$ by $3$ .

$\frac{6 x^{5} - 4 x^{2} + 5}{6 x^{2} + 8 x - 3 x - 1 \cdot 4}$

Step 8.2.15

Multiply $- 1$ by $4$ .

$\frac{6 x^{5} - 4 x^{2} + 5}{6 x^{2} + 8 x - 3 x - 4}$

Step 8.2.16

Subtract $3 x$ from $8 x$ .

$\frac{6 x^{5} - 4 x^{2} + 5}{6 x^{2} + 5 x - 4}$

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 $0$ .

$6 x^{2}$

$5 x$

$4$

$6 x^{5}$

$0 x^{4}$

$0 x^{3}$

$4 x^{2}$

$0 x$

$5$

Step 8.4

Divide the highest order term in the dividend $6 x^{5}$ by the highest order term in divisor $6 x^{2}$ .

$x^{3}$

$6 x^{2}$

$5 x$

$4$

$6 x^{5}$

$0 x^{4}$

$0 x^{3}$

$4 x^{2}$

$0 x$

$5$

Step 8.5

Multiply the new quotient term by the divisor.

$x^{3}$

$6 x^{2}$

$5 x$

$4$

$6 x^{5}$

$0 x^{4}$

$0 x^{3}$

$4 x^{2}$

$0 x$

$5$

$6 x^{5}$

$5 x^{4}$

$4 x^{3}$

Step 8.6

The expression needs to be subtracted from the dividend, so change all the signs in $6 x^{5} + 5 x^{4} - 4 x^{3}$

$x^{3}$

$6 x^{2}$

$5 x$

$4$

$6 x^{5}$

$0 x^{4}$

$0 x^{3}$

$4 x^{2}$

$0 x$

$5$

$6 x^{5}$

$5 x^{4}$

$4 x^{3}$

Step 8.7

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

$x^{3}$

$6 x^{2}$

$5 x$

$4$

$6 x^{5}$

$0 x^{4}$

$0 x^{3}$

$4 x^{2}$

$0 x$

$5$

$6 x^{5}$

$5 x^{4}$

$4 x^{3}$

$5 x^{4}$

$4 x^{3}$

Step 8.8

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

$x^{3}$

$6 x^{2}$

$5 x$

$4$

$6 x^{5}$

$0 x^{4}$

$0 x^{3}$

$4 x^{2}$

$0 x$

$5$

$6 x^{5}$

$5 x^{4}$

$4 x^{3}$

$5 x^{4}$

$4 x^{3}$

$4 x^{2}$

Step 8.9

Divide the highest order term in the dividend $- 5 x^{4}$ by the highest order term in divisor $6 x^{2}$ .

$x^{3}$

$\frac{5 x^{2}}{6}$

$6 x^{2}$

$5 x$

$4$

$6 x^{5}$

$0 x^{4}$

$0 x^{3}$

$4 x^{2}$

$0 x$

$5$

$6 x^{5}$

$5 x^{4}$

$4 x^{3}$

$5 x^{4}$

$4 x^{3}$

$4 x^{2}$

Step 8.10

Multiply the new quotient term by the divisor.

$x^{3}$

$\frac{5 x^{2}}{6}$

$6 x^{2}$

$5 x$

$4$

$6 x^{5}$

$0 x^{4}$

$0 x^{3}$

$4 x^{2}$

$0 x$

$5$

$6 x^{5}$

$5 x^{4}$

$4 x^{3}$

$5 x^{4}$

$4 x^{3}$

$4 x^{2}$

$5 x^{4}$

$\frac{25 x^{3}}{6}$

$\frac{10 x^{2}}{3}$

Step 8.11

The expression needs to be subtracted from the dividend, so change all the signs in $- 5 x^{4} - \frac{25 x^{3}}{6} + \frac{10 x^{2}}{3}$

$x^{3}$

$\frac{5 x^{2}}{6}$

$6 x^{2}$

$5 x$

$4$

$6 x^{5}$

$0 x^{4}$

$0 x^{3}$

$4 x^{2}$

$0 x$

$5$

$6 x^{5}$

$5 x^{4}$

$4 x^{3}$

$5 x^{4}$

$4 x^{3}$

$4 x^{2}$

$5 x^{4}$

$\frac{25 x^{3}}{6}$

$\frac{10 x^{2}}{3}$

Step 8.12

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

$x^{3}$

$\frac{5 x^{2}}{6}$

$6 x^{2}$

$5 x$

$4$

$6 x^{5}$

$0 x^{4}$

$0 x^{3}$

$4 x^{2}$

$0 x$

$5$

$6 x^{5}$

$5 x^{4}$

$4 x^{3}$

$5 x^{4}$

$4 x^{3}$

$4 x^{2}$

$5 x^{4}$

$\frac{25 x^{3}}{6}$

$\frac{10 x^{2}}{3}$

$\frac{49 x^{3}}{6}$

$\frac{22 x^{2}}{3}$

Step 8.13

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

$x^{3}$

$\frac{5 x^{2}}{6}$

$6 x^{2}$

$5 x$

$4$

$6 x^{5}$

$0 x^{4}$

$0 x^{3}$

$4 x^{2}$

$0 x$

$5$

$6 x^{5}$

$5 x^{4}$

$4 x^{3}$

$5 x^{4}$

$4 x^{3}$

$4 x^{2}$

$5 x^{4}$

$\frac{25 x^{3}}{6}$

$\frac{10 x^{2}}{3}$

$\frac{49 x^{3}}{6}$

$\frac{22 x^{2}}{3}$

$0 x$

Step 8.14

Divide the highest order term in the dividend $\frac{49 x^{3}}{6}$ by the highest order term in divisor $6 x^{2}$ .

$x^{3}$

$\frac{5 x^{2}}{6}$

$\frac{49 x}{36}$

$6 x^{2}$

$5 x$

$4$

$6 x^{5}$

$0 x^{4}$

$0 x^{3}$

$4 x^{2}$

$0 x$

$5$

$6 x^{5}$

$5 x^{4}$

$4 x^{3}$

$5 x^{4}$

$4 x^{3}$

$4 x^{2}$

$5 x^{4}$

$\frac{25 x^{3}}{6}$

$\frac{10 x^{2}}{3}$

$\frac{49 x^{3}}{6}$

$\frac{22 x^{2}}{3}$

$0 x$

Step 8.15

Multiply the new quotient term by the divisor.

$x^{3}$

$\frac{5 x^{2}}{6}$

$\frac{49 x}{36}$

$6 x^{2}$

$5 x$

$4$

$6 x^{5}$

$0 x^{4}$

$0 x^{3}$

$4 x^{2}$

$0 x$

$5$

$6 x^{5}$

$5 x^{4}$

$4 x^{3}$

$5 x^{4}$

$4 x^{3}$

$4 x^{2}$

$5 x^{4}$

$\frac{25 x^{3}}{6}$

$\frac{10 x^{2}}{3}$

$\frac{49 x^{3}}{6}$

$\frac{22 x^{2}}{3}$

$0 x$

$\frac{49 x^{3}}{6}$

$\frac{245 x^{2}}{36}$

$\frac{49 x}{9}$

Step 8.16

The expression needs to be subtracted from the dividend, so change all the signs in $\frac{49 x^{3}}{6} + \frac{245 x^{2}}{36} - \frac{49 x}{9}$

$x^{3}$

$\frac{5 x^{2}}{6}$

$\frac{49 x}{36}$

$6 x^{2}$

$5 x$

$4$

$6 x^{5}$

$0 x^{4}$

$0 x^{3}$

$4 x^{2}$

$0 x$

$5$

$6 x^{5}$

$5 x^{4}$

$4 x^{3}$

$5 x^{4}$

$4 x^{3}$

$4 x^{2}$

$5 x^{4}$

$\frac{25 x^{3}}{6}$

$\frac{10 x^{2}}{3}$

$\frac{49 x^{3}}{6}$

$\frac{22 x^{2}}{3}$

$0 x$

$\frac{49 x^{3}}{6}$

$\frac{245 x^{2}}{36}$

$\frac{49 x}{9}$

Step 8.17

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

$x^{3}$

$\frac{5 x^{2}}{6}$

$\frac{49 x}{36}$

$6 x^{2}$

$5 x$

$4$

$6 x^{5}$

$0 x^{4}$

$0 x^{3}$

$4 x^{2}$

$0 x$

$5$

$6 x^{5}$

$5 x^{4}$

$4 x^{3}$

$5 x^{4}$

$4 x^{3}$

$4 x^{2}$

$5 x^{4}$

$\frac{25 x^{3}}{6}$

$\frac{10 x^{2}}{3}$

$\frac{49 x^{3}}{6}$

$\frac{22 x^{2}}{3}$

$0 x$

$\frac{49 x^{3}}{6}$

$\frac{245 x^{2}}{36}$

$\frac{49 x}{9}$

$\frac{509 x^{2}}{36}$

$\frac{49 x}{9}$

Step 8.18

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

$x^{3}$

$\frac{5 x^{2}}{6}$

$\frac{49 x}{36}$

$6 x^{2}$

$5 x$

$4$

$6 x^{5}$

$0 x^{4}$

$0 x^{3}$

$4 x^{2}$

$0 x$

$5$

$6 x^{5}$

$5 x^{4}$

$4 x^{3}$

$5 x^{4}$

$4 x^{3}$

$4 x^{2}$

$5 x^{4}$

$\frac{25 x^{3}}{6}$

$\frac{10 x^{2}}{3}$

$\frac{49 x^{3}}{6}$

$\frac{22 x^{2}}{3}$

$0 x$

$\frac{49 x^{3}}{6}$

$\frac{245 x^{2}}{36}$

$\frac{49 x}{9}$

$\frac{509 x^{2}}{36}$

$\frac{49 x}{9}$

$5$

Step 8.19

Divide the highest order term in the dividend $- \frac{509 x^{2}}{36}$ by the highest order term in divisor $6 x^{2}$ .

$x^{3}$

$\frac{5 x^{2}}{6}$

$\frac{49 x}{36}$

$\frac{509}{216}$

$6 x^{2}$

$5 x$

$4$

$6 x^{5}$

$0 x^{4}$

$0 x^{3}$

$4 x^{2}$

$0 x$

$5$

$6 x^{5}$

$5 x^{4}$

$4 x^{3}$

$5 x^{4}$

$4 x^{3}$

$4 x^{2}$

$5 x^{4}$

$\frac{25 x^{3}}{6}$

$\frac{10 x^{2}}{3}$

$\frac{49 x^{3}}{6}$

$\frac{22 x^{2}}{3}$

$0 x$

$\frac{49 x^{3}}{6}$

$\frac{245 x^{2}}{36}$

$\frac{49 x}{9}$

$\frac{509 x^{2}}{36}$

$\frac{49 x}{9}$

$5$

Step 8.20

Multiply the new quotient term by the divisor.

$x^{3}$

$\frac{5 x^{2}}{6}$

$\frac{49 x}{36}$

$\frac{509}{216}$

$6 x^{2}$

$5 x$

$4$

$6 x^{5}$

$0 x^{4}$

$0 x^{3}$

$4 x^{2}$

$0 x$

$5$

$6 x^{5}$

$5 x^{4}$

$4 x^{3}$

$5 x^{4}$

$4 x^{3}$

$4 x^{2}$

$5 x^{4}$

$\frac{25 x^{3}}{6}$

$\frac{10 x^{2}}{3}$

$\frac{49 x^{3}}{6}$

$\frac{22 x^{2}}{3}$

$0 x$

$\frac{49 x^{3}}{6}$

$\frac{245 x^{2}}{36}$

$\frac{49 x}{9}$

$\frac{509 x^{2}}{36}$

$\frac{49 x}{9}$

$5$

$\frac{509 x^{2}}{36}$

$\frac{2545 x}{216}$

$\frac{509}{54}$

Step 8.21

The expression needs to be subtracted from the dividend, so change all the signs in $- \frac{509 x^{2}}{36} - \frac{2545 x}{216} + \frac{509}{54}$

$x^{3}$

$\frac{5 x^{2}}{6}$

$\frac{49 x}{36}$

$\frac{509}{216}$

$6 x^{2}$

$5 x$

$4$

$6 x^{5}$

$0 x^{4}$

$0 x^{3}$

$4 x^{2}$

$0 x$

$5$

$6 x^{5}$

$5 x^{4}$

$4 x^{3}$

$5 x^{4}$

$4 x^{3}$

$4 x^{2}$

$5 x^{4}$

$\frac{25 x^{3}}{6}$

$\frac{10 x^{2}}{3}$

$\frac{49 x^{3}}{6}$

$\frac{22 x^{2}}{3}$

$0 x$

$\frac{49 x^{3}}{6}$

$\frac{245 x^{2}}{36}$

$\frac{49 x}{9}$

$\frac{509 x^{2}}{36}$

$\frac{49 x}{9}$

$5$

$\frac{509 x^{2}}{36}$

$\frac{2545 x}{216}$

$\frac{509}{54}$

Step 8.22

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

$x^{3}$

$\frac{5 x^{2}}{6}$

$\frac{49 x}{36}$

$\frac{509}{216}$

$6 x^{2}$

$5 x$

$4$

$6 x^{5}$

$0 x^{4}$

$0 x^{3}$

$4 x^{2}$

$0 x$

$5$

$6 x^{5}$

$5 x^{4}$

$4 x^{3}$

$5 x^{4}$

$4 x^{3}$

$4 x^{2}$

$5 x^{4}$

$\frac{25 x^{3}}{6}$

$\frac{10 x^{2}}{3}$

$\frac{49 x^{3}}{6}$

$\frac{22 x^{2}}{3}$

$0 x$

$\frac{49 x^{3}}{6}$

$\frac{245 x^{2}}{36}$

$\frac{49 x}{9}$

$\frac{509 x^{2}}{36}$

$\frac{49 x}{9}$

$5$

$\frac{509 x^{2}}{36}$

$\frac{2545 x}{216}$

$\frac{509}{54}$

$\frac{3721 x}{216}$

$\frac{239}{54}$

Step 8.23

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

$x^{3} - \frac{5 x^{2}}{6} + \frac{49 x}{36} - \frac{509}{216} + \frac{\frac{3721 x}{216} - \frac{239}{54}}{6 x^{2} + 5 x - 4}$

Step 8.24

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

$y = x^{3} - \frac{5 x^{2}}{6} + \frac{49 x}{36} - \frac{509}{216}$

Step 9

This is the set of all asymptotes.

Vertical Asymptotes: $x = - \frac{4}{3}, \frac{1}{2}$

No Horizontal Asymptotes

Oblique Asymptotes: $y = x^{3} - \frac{5 x^{2}}{6} + \frac{49 x}{36} - \frac{509}{216}$

Step 10