Precalculus Examples

$2 x^{4} - 13 x^{3} - 16 x^{2} + 243 x - 116$

Step 1

Factor $2 x^{4} - 13 x^{3} - 16 x^{2} + 243 x - 116$ using the rational roots test.

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Step 1.1

If a polynomial function has integer coefficients, then every rational zero will have the form $\frac{p}{q}$ where $p$ is a factor of the constant and $q$ is a factor of the leading coefficient.

$p = \pm 1, \pm 116, \pm 2, \pm 58, \pm 4, \pm 29$

$q = \pm 1, \pm 2$

Step 1.2

Find every combination of $\pm \frac{p}{q}$ . These are the possible roots of the polynomial function.

$\pm 1, \pm 0.5, \pm 116, \pm 58, \pm 2, \pm 29, \pm 4, \pm 14.5$

Step 1.3

Substitute $0.5$ and simplify the expression. In this case, the expression is equal to $0$ so $0.5$ is a root of the polynomial.

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Step 1.3.1

Substitute $0.5$ into the polynomial.

$2 \cdot {0.5}^{4} - 13 \cdot {0.5}^{3} - 16 \cdot {0.5}^{2} + 243 \cdot 0.5 - 116$

Step 1.3.2

Raise $0.5$ to the power of $4$ .

$2 \cdot 0.0625 - 13 \cdot {0.5}^{3} - 16 \cdot {0.5}^{2} + 243 \cdot 0.5 - 116$

Step 1.3.3

Multiply $2$ by $0.0625$ .

$0.125 - 13 \cdot {0.5}^{3} - 16 \cdot {0.5}^{2} + 243 \cdot 0.5 - 116$

Step 1.3.4

Raise $0.5$ to the power of $3$ .

$0.125 - 13 \cdot 0.125 - 16 \cdot {0.5}^{2} + 243 \cdot 0.5 - 116$

Step 1.3.5

Multiply $- 13$ by $0.125$ .

$0.125 - 1.625 - 16 \cdot {0.5}^{2} + 243 \cdot 0.5 - 116$

Step 1.3.6

Subtract $1.625$ from $0.125$ .

$- 1.5 - 16 \cdot {0.5}^{2} + 243 \cdot 0.5 - 116$

Step 1.3.7

Raise $0.5$ to the power of $2$ .

$- 1.5 - 16 \cdot 0.25 + 243 \cdot 0.5 - 116$

Step 1.3.8

Multiply $- 16$ by $0.25$ .

$- 1.5 - 4 + 243 \cdot 0.5 - 116$

Step 1.3.9

Subtract $4$ from $- 1.5$ .

$- 5.5 + 243 \cdot 0.5 - 116$

Step 1.3.10

Multiply $243$ by $0.5$ .

$- 5.5 + 121.5 - 116$

Step 1.3.11

Add $- 5.5$ and $121.5$ .

$116 - 116$

Step 1.3.12

Subtract $116$ from $116$ .

$0$

Step 1.4

Since $0.5$ is a known root, divide the polynomial by $2 x - 1$ to find the quotient polynomial. This polynomial can then be used to find the remaining roots.

$\frac{2 x^{4} - 13 x^{3} - 16 x^{2} + 243 x - 116}{2 x - 1}$

Step 1.5

Divide $2 x^{4} - 13 x^{3} - 16 x^{2} + 243 x - 116$ by $2 x - 1$ .

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Step 1.5.1

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

$2 x$

$1$

$2 x^{4}$

$13 x^{3}$

$16 x^{2}$

$243 x$

$116$

Step 1.5.2

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

					$x^{3}$
	$2 x$	-	$1$		$2 x^{4}$	-	$13 x^{3}$	-	$16 x^{2}$	+	$243 x$	-	$116$

Step 1.5.3

Multiply the new quotient term by the divisor.

				$x^{3}$
$2 x$	-	$1$		$2 x^{4}$	-	$13 x^{3}$	-	$16 x^{2}$	+	$243 x$	-	$116$
			+	$2 x^{4}$	-	$x^{3}$

Step 1.5.4

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

				$x^{3}$
$2 x$	-	$1$		$2 x^{4}$	-	$13 x^{3}$	-	$16 x^{2}$	+	$243 x$	-	$116$
			-	$2 x^{4}$	+	$x^{3}$

Step 1.5.5

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

				$x^{3}$
$2 x$	-	$1$		$2 x^{4}$	-	$13 x^{3}$	-	$16 x^{2}$	+	$243 x$	-	$116$
			-	$2 x^{4}$	+	$x^{3}$
					-	$12 x^{3}$

Step 1.5.6

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

				$x^{3}$
$2 x$	-	$1$		$2 x^{4}$	-	$13 x^{3}$	-	$16 x^{2}$	+	$243 x$	-	$116$
			-	$2 x^{4}$	+	$x^{3}$
					-	$12 x^{3}$	-	$16 x^{2}$

Step 1.5.7

Divide the highest order term in the dividend $- 12 x^{3}$ by the highest order term in divisor $2 x$ .

				$x^{3}$	-	$6 x^{2}$
$2 x$	-	$1$		$2 x^{4}$	-	$13 x^{3}$	-	$16 x^{2}$	+	$243 x$	-	$116$
			-	$2 x^{4}$	+	$x^{3}$
					-	$12 x^{3}$	-	$16 x^{2}$

Step 1.5.8

Multiply the new quotient term by the divisor.

				$x^{3}$	-	$6 x^{2}$
$2 x$	-	$1$		$2 x^{4}$	-	$13 x^{3}$	-	$16 x^{2}$	+	$243 x$	-	$116$
			-	$2 x^{4}$	+	$x^{3}$
					-	$12 x^{3}$	-	$16 x^{2}$
					-	$12 x^{3}$	+	$6 x^{2}$

Step 1.5.9

The expression needs to be subtracted from the dividend, so change all the signs in $- 12 x^{3} + 6 x^{2}$

				$x^{3}$	-	$6 x^{2}$
$2 x$	-	$1$		$2 x^{4}$	-	$13 x^{3}$	-	$16 x^{2}$	+	$243 x$	-	$116$
			-	$2 x^{4}$	+	$x^{3}$
					-	$12 x^{3}$	-	$16 x^{2}$
					+	$12 x^{3}$	-	$6 x^{2}$

Step 1.5.10

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

				$x^{3}$	-	$6 x^{2}$
$2 x$	-	$1$		$2 x^{4}$	-	$13 x^{3}$	-	$16 x^{2}$	+	$243 x$	-	$116$
			-	$2 x^{4}$	+	$x^{3}$
					-	$12 x^{3}$	-	$16 x^{2}$
					+	$12 x^{3}$	-	$6 x^{2}$
							-	$22 x^{2}$

Step 1.5.11

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

$x^{3}$

$6 x^{2}$

$2 x$

$1$

$2 x^{4}$

$13 x^{3}$

$16 x^{2}$

$243 x$

$116$

$2 x^{4}$

$x^{3}$

$12 x^{3}$

$16 x^{2}$

$12 x^{3}$

$6 x^{2}$

$22 x^{2}$

$243 x$

Step 1.5.12

Divide the highest order term in the dividend $- 22 x^{2}$ by the highest order term in divisor $2 x$ .

$x^{3}$

$6 x^{2}$

$11 x$

$2 x$

$1$

$2 x^{4}$

$13 x^{3}$

$16 x^{2}$

$243 x$

$116$

$2 x^{4}$

$x^{3}$

$12 x^{3}$

$16 x^{2}$

$12 x^{3}$

$6 x^{2}$

$22 x^{2}$

$243 x$

Step 1.5.13

Multiply the new quotient term by the divisor.

$x^{3}$

$6 x^{2}$

$11 x$

$2 x$

$1$

$2 x^{4}$

$13 x^{3}$

$16 x^{2}$

$243 x$

$116$

$2 x^{4}$

$x^{3}$

$12 x^{3}$

$16 x^{2}$

$12 x^{3}$

$6 x^{2}$

$22 x^{2}$

$243 x$

$22 x^{2}$

$11 x$

Step 1.5.14

The expression needs to be subtracted from the dividend, so change all the signs in $- 22 x^{2} + 11 x$

$x^{3}$

$6 x^{2}$

$11 x$

$2 x$

$1$

$2 x^{4}$

$13 x^{3}$

$16 x^{2}$

$243 x$

$116$

$2 x^{4}$

$x^{3}$

$12 x^{3}$

$16 x^{2}$

$12 x^{3}$

$6 x^{2}$

$22 x^{2}$

$243 x$

$22 x^{2}$

$11 x$

Step 1.5.15

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

$x^{3}$

$6 x^{2}$

$11 x$

$2 x$

$1$

$2 x^{4}$

$13 x^{3}$

$16 x^{2}$

$243 x$

$116$

$2 x^{4}$

$x^{3}$

$12 x^{3}$

$16 x^{2}$

$12 x^{3}$

$6 x^{2}$

$22 x^{2}$

$243 x$

$22 x^{2}$

$11 x$

$232 x$

Step 1.5.16

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

$x^{3}$

$6 x^{2}$

$11 x$

$2 x$

$1$

$2 x^{4}$

$13 x^{3}$

$16 x^{2}$

$243 x$

$116$

$2 x^{4}$

$x^{3}$

$12 x^{3}$

$16 x^{2}$

$12 x^{3}$

$6 x^{2}$

$22 x^{2}$

$243 x$

$22 x^{2}$

$11 x$

$232 x$

$116$

Step 1.5.17

Divide the highest order term in the dividend $232 x$ by the highest order term in divisor $2 x$ .

$x^{3}$

$6 x^{2}$

$11 x$

$116$

$2 x$

$1$

$2 x^{4}$

$13 x^{3}$

$16 x^{2}$

$243 x$

$116$

$2 x^{4}$

$x^{3}$

$12 x^{3}$

$16 x^{2}$

$12 x^{3}$

$6 x^{2}$

$22 x^{2}$

$243 x$

$22 x^{2}$

$11 x$

$232 x$

$116$

Step 1.5.18

Multiply the new quotient term by the divisor.

				$x^{3}$	-	$6 x^{2}$	-	$11 x$	+	$116$
$2 x$	-	$1$		$2 x^{4}$	-	$13 x^{3}$	-	$16 x^{2}$	+	$243 x$	-	$116$
			-	$2 x^{4}$	+	$x^{3}$
					-	$12 x^{3}$	-	$16 x^{2}$
					+	$12 x^{3}$	-	$6 x^{2}$
							-	$22 x^{2}$	+	$243 x$
							+	$22 x^{2}$	-	$11 x$
									+	$232 x$	-	$116$
									+	$232 x$	-	$116$

Step 1.5.19

The expression needs to be subtracted from the dividend, so change all the signs in $232 x - 116$

				$x^{3}$	-	$6 x^{2}$	-	$11 x$	+	$116$
$2 x$	-	$1$		$2 x^{4}$	-	$13 x^{3}$	-	$16 x^{2}$	+	$243 x$	-	$116$
			-	$2 x^{4}$	+	$x^{3}$
					-	$12 x^{3}$	-	$16 x^{2}$
					+	$12 x^{3}$	-	$6 x^{2}$
							-	$22 x^{2}$	+	$243 x$
							+	$22 x^{2}$	-	$11 x$
									+	$232 x$	-	$116$
									-	$232 x$	+	$116$

Step 1.5.20

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

				$x^{3}$	-	$6 x^{2}$	-	$11 x$	+	$116$
$2 x$	-	$1$		$2 x^{4}$	-	$13 x^{3}$	-	$16 x^{2}$	+	$243 x$	-	$116$
			-	$2 x^{4}$	+	$x^{3}$
					-	$12 x^{3}$	-	$16 x^{2}$
					+	$12 x^{3}$	-	$6 x^{2}$
							-	$22 x^{2}$	+	$243 x$
							+	$22 x^{2}$	-	$11 x$
									+	$232 x$	-	$116$
									-	$232 x$	+	$116$
												$0$

Step 1.5.21

Since the remander is $0$ , the final answer is the quotient.

$x^{3} - 6 x^{2} - 11 x + 116$

Step 1.6

Write $2 x^{4} - 13 x^{3} - 16 x^{2} + 243 x - 116$ as a set of factors.

$(2 x - 1) (x^{3} - 6 x^{2} - 11 x + 116)$

Step 2

Factor $x^{3} - 6 x^{2} - 11 x + 116$ using the rational roots test.

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Step 2.1

Factor $x^{3} - 6 x^{2} - 11 x + 116$ using the rational roots test.

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Step 2.1.1

If a polynomial function has integer coefficients, then every rational zero will have the form $\frac{p}{q}$ where $p$ is a factor of the constant and $q$ is a factor of the leading coefficient.

$p = \pm 1, \pm 116, \pm 2, \pm 58, \pm 4, \pm 29$

$q = \pm 1$

Step 2.1.2

Find every combination of $\pm \frac{p}{q}$ . These are the possible roots of the polynomial function.

$\pm 1, \pm 116, \pm 2, \pm 58, \pm 4, \pm 29$

Step 2.1.3

Substitute $- 4$ and simplify the expression. In this case, the expression is equal to $0$ so $- 4$ is a root of the polynomial.

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Step 2.1.3.1

Substitute $- 4$ into the polynomial.

${(- 4)}^{3} - 6 {(- 4)}^{2} - 11 \cdot - 4 + 116$

Step 2.1.3.2

Raise $- 4$ to the power of $3$ .

$- 64 - 6 {(- 4)}^{2} - 11 \cdot - 4 + 116$

Step 2.1.3.3

Raise $- 4$ to the power of $2$ .

$- 64 - 6 \cdot 16 - 11 \cdot - 4 + 116$

Step 2.1.3.4

Multiply $- 6$ by $16$ .

$- 64 - 96 - 11 \cdot - 4 + 116$

Step 2.1.3.5

Subtract $96$ from $- 64$ .

$- 160 - 11 \cdot - 4 + 116$

Step 2.1.3.6

Multiply $- 11$ by $- 4$ .

$- 160 + 44 + 116$

Step 2.1.3.7

Add $- 160$ and $44$ .

$- 116 + 116$

Step 2.1.3.8

Add $- 116$ and $116$ .

$0$

Step 2.1.4

Since $- 4$ is a known root, divide the polynomial by $x + 4$ to find the quotient polynomial. This polynomial can then be used to find the remaining roots.

$\frac{x^{3} - 6 x^{2} - 11 x + 116}{x + 4}$

Step 2.1.5

Divide $x^{3} - 6 x^{2} - 11 x + 116$ by $x + 4$ .

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Step 2.1.5.1

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

$x$

$4$

$x^{3}$

$6 x^{2}$

$11 x$

$116$

Step 2.1.5.2

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

					$x^{2}$
	$x$	+	$4$		$x^{3}$	-	$6 x^{2}$	-	$11 x$	+	$116$

Step 2.1.5.3

Multiply the new quotient term by the divisor.

				$x^{2}$
$x$	+	$4$		$x^{3}$	-	$6 x^{2}$	-	$11 x$	+	$116$
			+	$x^{3}$	+	$4 x^{2}$

Step 2.1.5.4

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

				$x^{2}$
$x$	+	$4$		$x^{3}$	-	$6 x^{2}$	-	$11 x$	+	$116$
			-	$x^{3}$	-	$4 x^{2}$

Step 2.1.5.5

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

				$x^{2}$
$x$	+	$4$		$x^{3}$	-	$6 x^{2}$	-	$11 x$	+	$116$
			-	$x^{3}$	-	$4 x^{2}$
					-	$10 x^{2}$

Step 2.1.5.6

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

				$x^{2}$
$x$	+	$4$		$x^{3}$	-	$6 x^{2}$	-	$11 x$	+	$116$
			-	$x^{3}$	-	$4 x^{2}$
					-	$10 x^{2}$	-	$11 x$

Step 2.1.5.7

Divide the highest order term in the dividend $- 10 x^{2}$ by the highest order term in divisor $x$ .

				$x^{2}$	-	$10 x$
$x$	+	$4$		$x^{3}$	-	$6 x^{2}$	-	$11 x$	+	$116$
			-	$x^{3}$	-	$4 x^{2}$
					-	$10 x^{2}$	-	$11 x$

Step 2.1.5.8

Multiply the new quotient term by the divisor.

				$x^{2}$	-	$10 x$
$x$	+	$4$		$x^{3}$	-	$6 x^{2}$	-	$11 x$	+	$116$
			-	$x^{3}$	-	$4 x^{2}$
					-	$10 x^{2}$	-	$11 x$
					-	$10 x^{2}$	-	$40 x$

Step 2.1.5.9

The expression needs to be subtracted from the dividend, so change all the signs in $- 10 x^{2} - 40 x$

				$x^{2}$	-	$10 x$
$x$	+	$4$		$x^{3}$	-	$6 x^{2}$	-	$11 x$	+	$116$
			-	$x^{3}$	-	$4 x^{2}$
					-	$10 x^{2}$	-	$11 x$
					+	$10 x^{2}$	+	$40 x$

Step 2.1.5.10

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

				$x^{2}$	-	$10 x$
$x$	+	$4$		$x^{3}$	-	$6 x^{2}$	-	$11 x$	+	$116$
			-	$x^{3}$	-	$4 x^{2}$
					-	$10 x^{2}$	-	$11 x$
					+	$10 x^{2}$	+	$40 x$
							+	$29 x$

Step 2.1.5.11

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

				$x^{2}$	-	$10 x$
$x$	+	$4$		$x^{3}$	-	$6 x^{2}$	-	$11 x$	+	$116$
			-	$x^{3}$	-	$4 x^{2}$
					-	$10 x^{2}$	-	$11 x$
					+	$10 x^{2}$	+	$40 x$
							+	$29 x$	+	$116$

Step 2.1.5.12

Divide the highest order term in the dividend $29 x$ by the highest order term in divisor $x$ .

				$x^{2}$	-	$10 x$	+	$29$
$x$	+	$4$		$x^{3}$	-	$6 x^{2}$	-	$11 x$	+	$116$
			-	$x^{3}$	-	$4 x^{2}$
					-	$10 x^{2}$	-	$11 x$
					+	$10 x^{2}$	+	$40 x$
							+	$29 x$	+	$116$

Step 2.1.5.13

Multiply the new quotient term by the divisor.

				$x^{2}$	-	$10 x$	+	$29$
$x$	+	$4$		$x^{3}$	-	$6 x^{2}$	-	$11 x$	+	$116$
			-	$x^{3}$	-	$4 x^{2}$
					-	$10 x^{2}$	-	$11 x$
					+	$10 x^{2}$	+	$40 x$
							+	$29 x$	+	$116$
							+	$29 x$	+	$116$

Step 2.1.5.14

The expression needs to be subtracted from the dividend, so change all the signs in $29 x + 116$

				$x^{2}$	-	$10 x$	+	$29$
$x$	+	$4$		$x^{3}$	-	$6 x^{2}$	-	$11 x$	+	$116$
			-	$x^{3}$	-	$4 x^{2}$
					-	$10 x^{2}$	-	$11 x$
					+	$10 x^{2}$	+	$40 x$
							+	$29 x$	+	$116$
							-	$29 x$	-	$116$

Step 2.1.5.15

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

				$x^{2}$	-	$10 x$	+	$29$
$x$	+	$4$		$x^{3}$	-	$6 x^{2}$	-	$11 x$	+	$116$
			-	$x^{3}$	-	$4 x^{2}$
					-	$10 x^{2}$	-	$11 x$
					+	$10 x^{2}$	+	$40 x$
							+	$29 x$	+	$116$
							-	$29 x$	-	$116$
										$0$

Step 2.1.5.16

Since the remander is $0$ , the final answer is the quotient.

$x^{2} - 10 x + 29$

Step 2.1.6

Write $x^{3} - 6 x^{2} - 11 x + 116$ as a set of factors.

$(2 x - 1) ((x + 4) (x^{2} - 10 x + 29))$

Step 2.2

Remove unnecessary parentheses.

$(2 x - 1) (x + 4) (x^{2} - 10 x + 29)$