Precalculus Examples

$f (x) = \sqrt{1 - \frac{5}{x}}$

Step 1

Set the radicand in $\sqrt{1 - \frac{5}{x}}$ greater than or equal to $0$ to find where the expression is defined.

$1 - \frac{5}{x} \geq 0$

Step 2

Solve for $x$ .

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Step 2.1

Subtract $1$ from both sides of the inequality.

$- \frac{5}{x} \geq - 1$

Step 2.2

Multiply both sides by $x$ .

$- \frac{5}{x} x = - x$

Step 2.3

Simplify the left side.

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Step 2.3.1

Cancel the common factor of $x$ .

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Step 2.3.1.1

Move the leading negative in $- \frac{5}{x}$ into the numerator.

$\frac{- 5}{x} x = - x$

Step 2.3.1.2

Cancel the common factor.

$\frac{- 5}{x} x = - x$

Step 2.3.1.3

Rewrite the expression.

$- 5 = - x$

Step 2.4

Solve for $x$ .

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Step 2.4.1

Rewrite the equation as $- x = - 5$ .

$- x = - 5$

Step 2.4.2

Divide each term in $- x = - 5$ by $- 1$ and simplify.

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Step 2.4.2.1

Divide each term in $- x = - 5$ by $- 1$ .

$\frac{- x}{- 1} = \frac{- 5}{- 1}$

Step 2.4.2.2

Simplify the left side.

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Step 2.4.2.2.1

Dividing two negative values results in a positive value.

$\frac{x}{1} = \frac{- 5}{- 1}$

Step 2.4.2.2.2

Divide $x$ by $1$ .

$x = \frac{- 5}{- 1}$

Step 2.4.2.3

Simplify the right side.

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Step 2.4.2.3.1

Divide $- 5$ by $- 1$ .

$x = 5$

Step 2.5

Find the domain of $1 - \frac{5}{x}$ .

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Step 2.5.1

Set the denominator in $\frac{5}{x}$ equal to $0$ to find where the expression is undefined.

$x = 0$

Step 2.5.2

The domain is all values of $x$ that make the expression defined.

$(- \infty, 0) \cup (0, \infty)$

Step 2.6

Use each root to create test intervals.

$x < 0$

$0 < x < 5$

$x > 5$

Step 2.7

Choose a test value from each interval and plug this value into the original inequality to determine which intervals satisfy the inequality.

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Step 2.7.1

Test a value on the interval $x < 0$ to see if it makes the inequality true.

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Step 2.7.1.1

Choose a value on the interval $x < 0$ and see if this value makes the original inequality true.

$x = - 2$

Step 2.7.1.2

Replace $x$ with $- 2$ in the original inequality.

$1 - \frac{5}{- 2} \geq 0$

Step 2.7.1.3

The left side $3.5$ is greater than the right side $0$ , which means that the given statement is always true.

True

Step 2.7.2

Test a value on the interval $0 < x < 5$ to see if it makes the inequality true.

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Step 2.7.2.1

Choose a value on the interval $0 < x < 5$ and see if this value makes the original inequality true.

$x = 2$

Step 2.7.2.2

Replace $x$ with $2$ in the original inequality.

$1 - \frac{5}{2} \geq 0$

Step 2.7.2.3

The left side $- 1.5$ is less than the right side $0$ , which means that the given statement is false.

False

Step 2.7.3

Test a value on the interval $x > 5$ to see if it makes the inequality true.

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Step 2.7.3.1

Choose a value on the interval $x > 5$ and see if this value makes the original inequality true.

$x = 8$

Step 2.7.3.2

Replace $x$ with $8$ in the original inequality.

$1 - \frac{5}{8} \geq 0$

Step 2.7.3.3

The left side $0.375$ is greater than the right side $0$ , which means that the given statement is always true.

True

Step 2.7.4

Compare the intervals to determine which ones satisfy the original inequality.

$x < 0$ True

$0 < x < 5$ False

$x > 5$ True

$x < 0$ True

$0 < x < 5$ False

$x > 5$ True

Step 2.8

The solution consists of all of the true intervals.

$x < 0$ or $x \geq 5$

Step 3

Set the denominator in $\frac{5}{x}$ equal to $0$ to find where the expression is undefined.

$x = 0$

Step 4

The domain is all values of $x$ that make the expression defined.

Interval Notation:

$(- \infty, 0) \cup [5, \infty)$

Set-Builder Notation:

${x | x < 0, x \geq 5}$

Step 5