Precalculus Examples

$f (x) = x^{3} + 2 x^{2} - 5 x - 10$

Step 1

Set $x^{3} + 2 x^{2} - 5 x - 10$ equal to $0$ .

$x^{3} + 2 x^{2} - 5 x - 10 = 0$

Step 2

Solve for $x$ .

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Step 2.1

Factor the left side of the equation.

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Step 2.1.1

Factor out the greatest common factor from each group.

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Step 2.1.1.1

Group the first two terms and the last two terms.

$(x^{3} + 2 x^{2}) - 5 x - 10 = 0$

Step 2.1.1.2

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

$x^{2} (x + 2) - 5 (x + 2) = 0$

Step 2.1.2

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

$(x + 2) (x^{2} - 5) = 0$

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 $0$ .

$x + 2 = 0$

$x^{2} - 5 = 0$

Step 2.3

Set $x + 2$ equal to $0$ and solve for $x$ .

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Step 2.3.1

Set $x + 2$ equal to $0$ .

$x + 2 = 0$

Step 2.3.2

Subtract $2$ from both sides of the equation.

$x = - 2$

Step 2.4

Set $x^{2} - 5$ equal to $0$ and solve for $x$ .

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Step 2.4.1

Set $x^{2} - 5$ equal to $0$ .

$x^{2} - 5 = 0$

Step 2.4.2

Solve $x^{2} - 5 = 0$ for $x$ .

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Step 2.4.2.1

Add $5$ to both sides of the equation.

$x^{2} = 5$

Step 2.4.2.2

Take the specified root of both sides of the equation to eliminate the exponent on the left side.

$x = \pm \sqrt{5}$

Step 2.4.2.3

The complete solution is the result of both the positive and negative portions of the solution.

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Step 2.4.2.3.1

First, use the positive value of the $\pm$ to find the first solution.

$x = \sqrt{5}$

Step 2.4.2.3.2

Next, use the negative value of the $\pm$ to find the second solution.

$x = - \sqrt{5}$

Step 2.4.2.3.3

The complete solution is the result of both the positive and negative portions of the solution.

$x = \sqrt{5}, - \sqrt{5}$

Step 2.5

The final solution is all the values that make $(x + 2) (x^{2} - 5) = 0$ true.

$x = - 2, \sqrt{5}, - \sqrt{5}$

Step 3

The result can be shown in multiple forms.

Exact Form:

$x = - 2, \sqrt{5}, - \sqrt{5}$

Decimal Form:

$x = - 2, 2.23606797 \dots, - 2.23606797 \dots$

Step 4