Pre-Algebra Examples

$\frac{x - 9}{x + 6} < 0$

Step 1

Find all the values where the expression switches from negative to positive by setting each factor equal to $0$ and solving.

$x - 9 = 0$

$x + 6 = 0$

Step 2

Add $9$ to both sides of the equation.

$x = 9$

Step 3

Subtract $6$ from both sides of the equation.

$x = - 6$

Step 4

Solve for each factor to find the values where the absolute value expression goes from negative to positive.

$x = 9$

$x = - 6$

Step 5

Consolidate the solutions.

$x = 9, - 6$

Step 6

Find the domain of $\frac{x - 9}{x + 6}$ .

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Step 6.1

Set the denominator in $\frac{x - 9}{x + 6}$ equal to $0$ to find where the expression is undefined.

$x + 6 = 0$

Step 6.2

Subtract $6$ from both sides of the equation.

$x = - 6$

Step 6.3

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

$(- \infty, - 6) \cup (- 6, \infty)$

Step 7

Use each root to create test intervals.

$x < - 6$

$- 6 < x < 9$

$x > 9$

Step 8

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 8.1

Test a value on the interval $x < - 6$ to see if it makes the inequality true.

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Step 8.1.1

Choose a value on the interval $x < - 6$ and see if this value makes the original inequality true.

$x = - 8$

Step 8.1.2

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

$\frac{(- 8) - 9}{(- 8) + 6} < 0$

Step 8.1.3

The left side $8.5$ is not less than the right side $0$ , which means that the given statement is false.

False

Step 8.2

Test a value on the interval $- 6 < x < 9$ to see if it makes the inequality true.

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Step 8.2.1

Choose a value on the interval $- 6 < x < 9$ and see if this value makes the original inequality true.

$x = 0$

Step 8.2.2

Replace $x$ with $0$ in the original inequality.

$\frac{(0) - 9}{(0) + 6} < 0$

Step 8.2.3

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

True

Step 8.3

Test a value on the interval $x > 9$ to see if it makes the inequality true.

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Step 8.3.1

Choose a value on the interval $x > 9$ and see if this value makes the original inequality true.

$x = 12$

Step 8.3.2

Replace $x$ with $12$ in the original inequality.

$\frac{(12) - 9}{(12) + 6} < 0$

Step 8.3.3

The left side $0.1\overline{6}$ is not less than the right side $0$ , which means that the given statement is false.

False

Step 8.4

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

$x < - 6$ False

$- 6 < x < 9$ True

$x > 9$ False

$x < - 6$ False

$- 6 < x < 9$ True

$x > 9$ False

Step 9

The solution consists of all of the true intervals.

$- 6 < x < 9$

Step 10