Precalculus Examples

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

Step 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.

$p = \pm 1, \pm 4, \pm 2$

$q = \pm 1$

Step 2

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

$\pm 1, \pm 4, \pm 2$

Step 3

Substitute $2$ and simplify the expression. In this case, the expression is equal to $0$ so $2$ is a root of the polynomial.

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Step 3.1

Substitute $2$ into the polynomial.

$2^{3} - 6 \cdot 2^{2} + 10 \cdot 2 - 4$

Step 3.2

Raise $2$ to the power of $3$ .

$8 - 6 \cdot 2^{2} + 10 \cdot 2 - 4$

Step 3.3

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

$8 - 6 \cdot 4 + 10 \cdot 2 - 4$

Step 3.4

Multiply $- 6$ by $4$ .

$8 - 24 + 10 \cdot 2 - 4$

Step 3.5

Subtract $24$ from $8$ .

$- 16 + 10 \cdot 2 - 4$

Step 3.6

Multiply $10$ by $2$ .

$- 16 + 20 - 4$

Step 3.7

Add $- 16$ and $20$ .

$4 - 4$

Step 3.8

Subtract $4$ from $4$ .

$0$

Step 4

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

$\frac{x^{3} - 6 x^{2} + 10 x - 4}{x - 2}$

Step 5

Divide $x^{3} - 6 x^{2} + 10 x - 4$ by $x - 2$ .

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Step 5.1

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

$x$

$2$

$x^{3}$

$6 x^{2}$

$10 x$

$4$

Step 5.2

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

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

Step 5.3

Multiply the new quotient term by the divisor.

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

Step 5.4

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

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

Step 5.5

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

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

Step 5.6

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

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

Step 5.7

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

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

Step 5.8

Multiply the new quotient term by the divisor.

				$x^{2}$	-	$4 x$
$x$	-	$2$		$x^{3}$	-	$6 x^{2}$	+	$10 x$	-	$4$
			-	$x^{3}$	+	$2 x^{2}$
					-	$4 x^{2}$	+	$10 x$
					-	$4 x^{2}$	+	$8 x$

Step 5.9

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

				$x^{2}$	-	$4 x$
$x$	-	$2$		$x^{3}$	-	$6 x^{2}$	+	$10 x$	-	$4$
			-	$x^{3}$	+	$2 x^{2}$
					-	$4 x^{2}$	+	$10 x$
					+	$4 x^{2}$	-	$8 x$

Step 5.10

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

				$x^{2}$	-	$4 x$
$x$	-	$2$		$x^{3}$	-	$6 x^{2}$	+	$10 x$	-	$4$
			-	$x^{3}$	+	$2 x^{2}$
					-	$4 x^{2}$	+	$10 x$
					+	$4 x^{2}$	-	$8 x$
							+	$2 x$

Step 5.11

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

				$x^{2}$	-	$4 x$
$x$	-	$2$		$x^{3}$	-	$6 x^{2}$	+	$10 x$	-	$4$
			-	$x^{3}$	+	$2 x^{2}$
					-	$4 x^{2}$	+	$10 x$
					+	$4 x^{2}$	-	$8 x$
							+	$2 x$	-	$4$

Step 5.12

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

				$x^{2}$	-	$4 x$	+	$2$
$x$	-	$2$		$x^{3}$	-	$6 x^{2}$	+	$10 x$	-	$4$
			-	$x^{3}$	+	$2 x^{2}$
					-	$4 x^{2}$	+	$10 x$
					+	$4 x^{2}$	-	$8 x$
							+	$2 x$	-	$4$

Step 5.13

Multiply the new quotient term by the divisor.

				$x^{2}$	-	$4 x$	+	$2$
$x$	-	$2$		$x^{3}$	-	$6 x^{2}$	+	$10 x$	-	$4$
			-	$x^{3}$	+	$2 x^{2}$
					-	$4 x^{2}$	+	$10 x$
					+	$4 x^{2}$	-	$8 x$
							+	$2 x$	-	$4$
							+	$2 x$	-	$4$

Step 5.14

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

				$x^{2}$	-	$4 x$	+	$2$
$x$	-	$2$		$x^{3}$	-	$6 x^{2}$	+	$10 x$	-	$4$
			-	$x^{3}$	+	$2 x^{2}$
					-	$4 x^{2}$	+	$10 x$
					+	$4 x^{2}$	-	$8 x$
							+	$2 x$	-	$4$
							-	$2 x$	+	$4$

Step 5.15

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

				$x^{2}$	-	$4 x$	+	$2$
$x$	-	$2$		$x^{3}$	-	$6 x^{2}$	+	$10 x$	-	$4$
			-	$x^{3}$	+	$2 x^{2}$
					-	$4 x^{2}$	+	$10 x$
					+	$4 x^{2}$	-	$8 x$
							+	$2 x$	-	$4$
							-	$2 x$	+	$4$
										$0$

Step 5.16

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

$x^{2} - 4 x + 2$

Step 6

Write $x^{3} - 6 x^{2} + 10 x - 4$ as a set of factors.

$(x - 2) (x^{2} - 4 x + 2)$