Trigonometry Examples

$3 x^{2} + 8 x - 16 > 0$

Step 1

Convert the inequality to an equation.

$3 x^{2} + 8 x - 16 = 0$

Step 2

Factor by grouping.

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Step 2.1

For a polynomial of the form $a x^{2} + b x + c$ , rewrite the middle term as a sum of two terms whose product is $a \cdot c = 3 \cdot - 16 = - 48$ and whose sum is $b = 8$ .

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Step 2.1.1

Factor $8$ out of $8 x$ .

$3 x^{2} + 8 (x) - 16 = 0$

Step 2.1.2

Rewrite $8$ as $- 4$ plus $12$

$3 x^{2} + (- 4 + 12) x - 16 = 0$

Step 2.1.3

Apply the distributive property.

$3 x^{2} - 4 x + 12 x - 16 = 0$

Step 2.2

Factor out the greatest common factor from each group.

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Step 2.2.1

Group the first two terms and the last two terms.

$(3 x^{2} - 4 x) + 12 x - 16 = 0$

Step 2.2.2

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

$x (3 x - 4) + 4 (3 x - 4) = 0$

Step 2.3

Factor the polynomial by factoring out the greatest common factor, $3 x - 4$ .

$(3 x - 4) (x + 4) = 0$

Step 3

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

$3 x - 4 = 0$

$x + 4 = 0$

Step 4

Set $3 x - 4$ equal to $0$ and solve for $x$ .

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Step 4.1

Set $3 x - 4$ equal to $0$ .

$3 x - 4 = 0$

Step 4.2

Solve $3 x - 4 = 0$ for $x$ .

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Step 4.2.1

Add $4$ to both sides of the equation.

$3 x = 4$

Step 4.2.2

Divide each term in $3 x = 4$ by $3$ and simplify.

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Step 4.2.2.1

Divide each term in $3 x = 4$ by $3$ .

$\frac{3 x}{3} = \frac{4}{3}$

Step 4.2.2.2

Simplify the left side.

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Step 4.2.2.2.1

Cancel the common factor of $3$ .

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Step 4.2.2.2.1.1

Cancel the common factor.

$\frac{3 x}{3} = \frac{4}{3}$

Step 4.2.2.2.1.2

Divide $x$ by $1$ .

$x = \frac{4}{3}$

Step 5

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

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Step 5.1

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

$x + 4 = 0$

Step 5.2

Subtract $4$ from both sides of the equation.

$x = - 4$

Step 6

The final solution is all the values that make $(3 x - 4) (x + 4) = 0$ true.

$x = \frac{4}{3}, - 4$

Step 7

Use each root to create test intervals.

$x < - 4$

$- 4 < x < \frac{4}{3}$

$x > \frac{4}{3}$

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 $x < - 4$ to see if it makes the inequality true.

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Step 8.1.1

Choose a value on the interval $x < - 4$ and see if this value makes the original inequality true.

$x = - 6$

Step 8.1.2

Replace $x$ with $- 6$ in the original inequality.

$3 {(- 6)}^{2} + 8 (- 6) - 16 > 0$

Step 8.1.3

The left side $44$ is greater than the right side $0$ , which means that the given statement is always true.

True

Step 8.2

Test a value on the interval $- 4 < x < \frac{4}{3}$ to see if it makes the inequality true.

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Step 8.2.1

Choose a value on the interval $- 4 < x < \frac{4}{3}$ and see if this value makes the original inequality true.

$x = 0$

Step 8.2.2

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

$3 {(0)}^{2} + 8 (0) - 16 > 0$

Step 8.2.3

The left side $- 16$ is not greater than the right side $0$ , which means that the given statement is false.

False

Step 8.3

Test a value on the interval $x > \frac{4}{3}$ to see if it makes the inequality true.

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Step 8.3.1

Choose a value on the interval $x > \frac{4}{3}$ and see if this value makes the original inequality true.

$x = 4$

Step 8.3.2

Replace $x$ with $4$ in the original inequality.

$3 {(4)}^{2} + 8 (4) - 16 > 0$

Step 8.3.3

The left side $64$ is greater than the right side $0$ , which means that the given statement is always true.

True

Step 8.4

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

$x < - 4$ True

$- 4 < x < \frac{4}{3}$ False

$x > \frac{4}{3}$ True

$x < - 4$ True

$- 4 < x < \frac{4}{3}$ False

$x > \frac{4}{3}$ True

Step 9

The solution consists of all of the true intervals.

$x < - 4$ or $x > \frac{4}{3}$

Step 10

The result can be shown in multiple forms.

Inequality Form:

$x < - 4 or x > \frac{4}{3}$

Interval Notation:

$(- \infty, - 4) \cup (\frac{4}{3}, \infty)$

Step 11