Precalculus Examples

$f (x) = \sqrt{x^{2} - 16}$

Step 1

Set the radicand in

$\sqrt{x^{2} - 16}$ greater than or equal to

$0$ to find where the expression is defined.

$x^{2} - 16 \geq 0$

Step 2

Solve for

$x$ .

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Step 2.1

Add

$16$ to both sides of the inequality.

$x^{2} \geq 16$

Step 2.2

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

$\sqrt{x^{2}} \geq \sqrt{16}$

Step 2.3

Simplify the equation.

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Step 2.3.1

Simplify the left side.

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Step 2.3.1.1

Pull terms out from under the radical.

$| x | \geq \sqrt{16}$

Step 2.3.2

Simplify the right side.

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Step 2.3.2.1

Simplify

$\sqrt{16}$ .

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Step 2.3.2.1.1

Rewrite

$16$ as

$4^{2}$ .

$| x | \geq \sqrt{4^{2}}$

Step 2.3.2.1.2

Pull terms out from under the radical.

$| x | \geq | 4 |$

Step 2.3.2.1.3

The absolute value is the distance between a number and zero. The distance between

$0$ and

$4$ is

$4$ .

$| x | \geq 4$

Step 2.4

Write

$| x | \geq 4$ as a piecewise.

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Step 2.4.1

To find the interval for the first piece, find where the inside of the absolute value is non-negative.

$x \geq 0$

Step 2.4.2

In the piece where

$x$ is non-negative, remove the absolute value.

$x \geq 4$

Step 2.4.3

To find the interval for the second piece, find where the inside of the absolute value is negative.

$x < 0$

Step 2.4.4

In the piece where

$x$ is negative, remove the absolute value and multiply by

$- 1$ .

$- x \geq 4$

Step 2.4.5

Write as a piecewise.

${\begin{cases} x \geq 4 & x \geq 0 \\ - x \geq 4 & x < 0 \end{cases}$

Step 2.5

Find the intersection of

$x \geq 4$ and

$x \geq 0$ .

$x \geq 4$

Step 2.6

Divide each term in

$- x \geq 4$ by

$- 1$ and simplify.

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Step 2.6.1

Divide each term in

$- x \geq 4$ by

$- 1$ . When multiplying or dividing both sides of an inequality by a negative value, flip the direction of the inequality sign.

$\frac{- x}{- 1} \leq \frac{4}{- 1}$

Step 2.6.2

Simplify the left side.

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Step 2.6.2.1

Dividing two negative values results in a positive value.

$\frac{x}{1} \leq \frac{4}{- 1}$

Step 2.6.2.2

Divide

$x$ by

$1$ .

$x \leq \frac{4}{- 1}$

Step 2.6.3

Simplify the right side.

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Step 2.6.3.1

Divide

$4$ by

$- 1$ .

$x \leq - 4$

Step 2.7

Find the union of the solutions.

$x \leq - 4$ or

$x \geq 4$

$x \leq - 4$ or

$x \geq 4$

Step 3

The domain is all values of

$x$ that make the expression defined.

Interval Notation:

$(- \infty, - 4] \cup [4, \infty)$

Set-Builder Notation:

${x | x \leq - 4, x \geq 4}$

Step 4