Precalculus Examples

$f (x) = x^{3} + 3 x^{2} - 219 x - 221$

Step 1

Set $x^{3} + 3 x^{2} - 219 x - 221$ equal to $0$ .

$x^{3} + 3 x^{2} - 219 x - 221 = 0$

Step 2

Solve for $x$ .

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Step 2.1

Factor $x^{3} + 3 x^{2} - 219 x - 221$ 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.

$p = \pm 1, \pm 221, \pm 13, \pm 17$

$q = \pm 1$

Step 2.1.2

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

$\pm 1, \pm 221, \pm 13, \pm 17$

Step 2.1.3

Substitute $- 1$ and simplify the expression. In this case, the expression is equal to $0$ so $- 1$ is a root of the polynomial.

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Step 2.1.3.1

Substitute $- 1$ into the polynomial.

${(- 1)}^{3} + 3 {(- 1)}^{2} - 219 \cdot - 1 - 221$

Step 2.1.3.2

Raise $- 1$ to the power of $3$ .

$- 1 + 3 {(- 1)}^{2} - 219 \cdot - 1 - 221$

Step 2.1.3.3

Raise $- 1$ to the power of $2$ .

$- 1 + 3 \cdot 1 - 219 \cdot - 1 - 221$

Step 2.1.3.4

Multiply $3$ by $1$ .

$- 1 + 3 - 219 \cdot - 1 - 221$

Step 2.1.3.5

Add $- 1$ and $3$ .

$2 - 219 \cdot - 1 - 221$

Step 2.1.3.6

Multiply $- 219$ by $- 1$ .

$2 + 219 - 221$

Step 2.1.3.7

Add $2$ and $219$ .

$221 - 221$

Step 2.1.3.8

Subtract $221$ from $221$ .

$0$

Step 2.1.4

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

$\frac{x^{3} + 3 x^{2} - 219 x - 221}{x + 1}$

Step 2.1.5

Divide $x^{3} + 3 x^{2} - 219 x - 221$ by $x + 1$ .

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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 $0$ .

$x$

$1$

$x^{3}$

$3 x^{2}$

$219 x$

$221$

Step 2.1.5.2

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

					$x^{2}$
	$x$	+	$1$		$x^{3}$	+	$3 x^{2}$	-	$219 x$	-	$221$

Step 2.1.5.3

Multiply the new quotient term by the divisor.

				$x^{2}$
$x$	+	$1$		$x^{3}$	+	$3 x^{2}$	-	$219 x$	-	$221$
			+	$x^{3}$	+	$x^{2}$

Step 2.1.5.4

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

				$x^{2}$
$x$	+	$1$		$x^{3}$	+	$3 x^{2}$	-	$219 x$	-	$221$
			-	$x^{3}$	-	$x^{2}$

Step 2.1.5.5

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

				$x^{2}$
$x$	+	$1$		$x^{3}$	+	$3 x^{2}$	-	$219 x$	-	$221$
			-	$x^{3}$	-	$x^{2}$
					+	$2 x^{2}$

Step 2.1.5.6

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

				$x^{2}$
$x$	+	$1$		$x^{3}$	+	$3 x^{2}$	-	$219 x$	-	$221$
			-	$x^{3}$	-	$x^{2}$
					+	$2 x^{2}$	-	$219 x$

Step 2.1.5.7

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

				$x^{2}$	+	$2 x$
$x$	+	$1$		$x^{3}$	+	$3 x^{2}$	-	$219 x$	-	$221$
			-	$x^{3}$	-	$x^{2}$
					+	$2 x^{2}$	-	$219 x$

Step 2.1.5.8

Multiply the new quotient term by the divisor.

				$x^{2}$	+	$2 x$
$x$	+	$1$		$x^{3}$	+	$3 x^{2}$	-	$219 x$	-	$221$
			-	$x^{3}$	-	$x^{2}$
					+	$2 x^{2}$	-	$219 x$
					+	$2 x^{2}$	+	$2 x$

Step 2.1.5.9

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

				$x^{2}$	+	$2 x$
$x$	+	$1$		$x^{3}$	+	$3 x^{2}$	-	$219 x$	-	$221$
			-	$x^{3}$	-	$x^{2}$
					+	$2 x^{2}$	-	$219 x$
					-	$2 x^{2}$	-	$2 x$

Step 2.1.5.10

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

				$x^{2}$	+	$2 x$
$x$	+	$1$		$x^{3}$	+	$3 x^{2}$	-	$219 x$	-	$221$
			-	$x^{3}$	-	$x^{2}$
					+	$2 x^{2}$	-	$219 x$
					-	$2 x^{2}$	-	$2 x$
							-	$221 x$

Step 2.1.5.11

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

				$x^{2}$	+	$2 x$
$x$	+	$1$		$x^{3}$	+	$3 x^{2}$	-	$219 x$	-	$221$
			-	$x^{3}$	-	$x^{2}$
					+	$2 x^{2}$	-	$219 x$
					-	$2 x^{2}$	-	$2 x$
							-	$221 x$	-	$221$

Step 2.1.5.12

Divide the highest order term in the dividend $- 221 x$ by the highest order term in divisor $x$ .

				$x^{2}$	+	$2 x$	-	$221$
$x$	+	$1$		$x^{3}$	+	$3 x^{2}$	-	$219 x$	-	$221$
			-	$x^{3}$	-	$x^{2}$
					+	$2 x^{2}$	-	$219 x$
					-	$2 x^{2}$	-	$2 x$
							-	$221 x$	-	$221$

Step 2.1.5.13

Multiply the new quotient term by the divisor.

				$x^{2}$	+	$2 x$	-	$221$
$x$	+	$1$		$x^{3}$	+	$3 x^{2}$	-	$219 x$	-	$221$
			-	$x^{3}$	-	$x^{2}$
					+	$2 x^{2}$	-	$219 x$
					-	$2 x^{2}$	-	$2 x$
							-	$221 x$	-	$221$
							-	$221 x$	-	$221$

Step 2.1.5.14

The expression needs to be subtracted from the dividend, so change all the signs in $- 221 x - 221$

				$x^{2}$	+	$2 x$	-	$221$
$x$	+	$1$		$x^{3}$	+	$3 x^{2}$	-	$219 x$	-	$221$
			-	$x^{3}$	-	$x^{2}$
					+	$2 x^{2}$	-	$219 x$
					-	$2 x^{2}$	-	$2 x$
							-	$221 x$	-	$221$
							+	$221 x$	+	$221$

Step 2.1.5.15

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

				$x^{2}$	+	$2 x$	-	$221$
$x$	+	$1$		$x^{3}$	+	$3 x^{2}$	-	$219 x$	-	$221$
			-	$x^{3}$	-	$x^{2}$
					+	$2 x^{2}$	-	$219 x$
					-	$2 x^{2}$	-	$2 x$
							-	$221 x$	-	$221$
							+	$221 x$	+	$221$
										$0$

Step 2.1.5.16

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

$x^{2} + 2 x - 221$

Step 2.1.6

Write $x^{3} + 3 x^{2} - 219 x - 221$ as a set of factors.

$(x + 1) (x^{2} + 2 x - 221) = 0$

Step 2.2

If any individual factor on the left side of the equation is equal to $0$ , the entire expression will be equal to $0$ .

$x + 1 = 0$

$x^{2} + 2 x - 221 = 0$

Step 2.3

Set $x + 1$ equal to $0$ and solve for $x$ .

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Step 2.3.1

Set $x + 1$ equal to $0$ .

$x + 1 = 0$

Step 2.3.2

Subtract $1$ from both sides of the equation.

$x = - 1$

Step 2.4

Set $x^{2} + 2 x - 221$ equal to $0$ and solve for $x$ .

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Step 2.4.1

Set $x^{2} + 2 x - 221$ equal to $0$ .

$x^{2} + 2 x - 221 = 0$

Step 2.4.2

Solve $x^{2} + 2 x - 221 = 0$ for $x$ .

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Step 2.4.2.1

Use the quadratic formula to find the solutions.

$\frac{- b \pm \sqrt{b^{2} - 4 (a c)}}{2 a}$

Step 2.4.2.2

Substitute the values $a = 1$ , $b = 2$ , and $c = - 221$ into the quadratic formula and solve for $x$ .

$\frac{- 2 \pm \sqrt{2^{2} - 4 \cdot (1 \cdot - 221)}}{2 \cdot 1}$

Step 2.4.2.3

Simplify.

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Step 2.4.2.3.1

Simplify the numerator.

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Step 2.4.2.3.1.1

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

$x = \frac{- 2 \pm \sqrt{4 - 4 \cdot 1 \cdot - 221}}{2 \cdot 1}$

Step 2.4.2.3.1.2

Multiply $- 4 \cdot 1 \cdot - 221$ .

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Step 2.4.2.3.1.2.1

Multiply $- 4$ by $1$ .

$x = \frac{- 2 \pm \sqrt{4 - 4 \cdot - 221}}{2 \cdot 1}$

Step 2.4.2.3.1.2.2

Multiply $- 4$ by $- 221$ .

$x = \frac{- 2 \pm \sqrt{4 + 884}}{2 \cdot 1}$

Step 2.4.2.3.1.3

Add $4$ and $884$ .

$x = \frac{- 2 \pm \sqrt{888}}{2 \cdot 1}$

Step 2.4.2.3.1.4

Rewrite $888$ as $2^{2} \cdot 222$ .

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Step 2.4.2.3.1.4.1

Factor $4$ out of $888$ .

$x = \frac{- 2 \pm \sqrt{4 (222)}}{2 \cdot 1}$

Step 2.4.2.3.1.4.2

Rewrite $4$ as $2^{2}$ .

$x = \frac{- 2 \pm \sqrt{2^{2} \cdot 222}}{2 \cdot 1}$

Step 2.4.2.3.1.5

Pull terms out from under the radical.

$x = \frac{- 2 \pm 2 \sqrt{222}}{2 \cdot 1}$

Step 2.4.2.3.2

Multiply $2$ by $1$ .

$x = \frac{- 2 \pm 2 \sqrt{222}}{2}$

Step 2.4.2.3.3

Simplify $\frac{- 2 \pm 2 \sqrt{222}}{2}$ .

$x = - 1 \pm \sqrt{222}$

Step 2.4.2.4

The final answer is the combination of both solutions.

$x = - 1 + \sqrt{222}, - 1 - \sqrt{222}$

Step 2.5

The final solution is all the values that make $(x + 1) (x^{2} + 2 x - 221) = 0$ true.

$x = - 1, - 1 + \sqrt{222}, - 1 - \sqrt{222}$

Step 3

The result can be shown in multiple forms.

Exact Form:

$x = - 1, - 1 + \sqrt{222}, - 1 - \sqrt{222}$

Decimal Form:

$x = - 1, 13.89966442 \dots, - 15.89966442 \dots$

Step 4