Trigonometry Examples

$f (x) = \frac{21}{(x + 8) (x - 4)}$

Step 1

Set the denominator in $\frac{21}{(x + 8) (x - 4)}$ equal to $0$ to find where the expression is undefined.

$(x + 8) (x - 4) = 0$

Step 2

Solve for $x$ .

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Step 2.1

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

$x + 8 = 0$

$x - 4 = 0$

Step 2.2

Set $x + 8$ equal to $0$ and solve for $x$ .

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Step 2.2.1

Set $x + 8$ equal to $0$ .

$x + 8 = 0$

Step 2.2.2

Subtract $8$ from both sides of the equation.

$x = - 8$

Step 2.3

Set $x - 4$ equal to $0$ and solve for $x$ .

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Step 2.3.1

Set $x - 4$ equal to $0$ .

$x - 4 = 0$

Step 2.3.2

Add $4$ to both sides of the equation.

$x = 4$

Step 2.4

The final solution is all the values that make $(x + 8) (x - 4) = 0$ true.

$x = - 8, 4$

Step 3

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

Interval Notation:

$(- \infty, - 8) \cup (- 8, 4) \cup (4, \infty)$

Set-Builder Notation:

${x | x \neq 4, - 8}$

Step 4