Precalculus Examples

$3 x^{2} - 5 x - 2 < 0$

Step 1

Convert the inequality to an equation.

$3 x^{2} - 5 x - 2 = 0$

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 $a \cdot c = 3 \cdot - 2 = - 6$ and whose sum is $b = - 5$ .

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Step 2.1.1

Factor $- 5$ out of $- 5 x$ .

$3 x^{2} - 5 x - 2 = 0$

Step 2.1.2

Rewrite $- 5$ as $1$ plus $- 6$

$3 x^{2} + (1 - 6) x - 2 = 0$

Step 2.1.3

Apply the distributive property.

$3 x^{2} + 1 x - 6 x - 2 = 0$

Step 2.1.4

Multiply $x$ by $1$ .

$3 x^{2} + x - 6 x - 2 = 0$

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.

$(3 x^{2} + x) - 6 x - 2 = 0$

Step 2.2.2

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

$x (3 x + 1) - 2 (3 x + 1) = 0$

Step 2.3

Factor the polynomial by factoring out the greatest common factor, $3 x + 1$ .

$(3 x + 1) (x - 2) = 0$

Step 3

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

$3 x + 1 = 0$

$x - 2 = 0$

Step 4

Set $3 x + 1$ equal to $0$ and solve for $x$ .

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Step 4.1

Set $3 x + 1$ equal to $0$ .

$3 x + 1 = 0$

Step 4.2

Solve $3 x + 1 = 0$ for $x$ .

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Step 4.2.1

Subtract $1$ from both sides of the equation.

$3 x = - 1$

Step 4.2.2

Divide each term in $3 x = - 1$ by $3$ and simplify.

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Step 4.2.2.1

Divide each term in $3 x = - 1$ by $3$ .

$\frac{3 x}{3} = \frac{- 1}{3}$

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.

$\frac{3 x}{3} = \frac{- 1}{3}$

Step 4.2.2.2.1.2

Divide $x$ by $1$ .

$x = \frac{- 1}{3}$

Step 4.2.2.3

Simplify the right side.

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Step 4.2.2.3.1

Move the negative in front of the fraction.

$x = - \frac{1}{3}$

Step 5

Set $x - 2$ equal to $0$ and solve for $x$ .

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Step 5.1

Set $x - 2$ equal to $0$ .

$x - 2 = 0$

Step 5.2

Add $2$ to both sides of the equation.

$x = 2$

Step 6

The final solution is all the values that make $(3 x + 1) (x - 2) = 0$ true.

$x = - \frac{1}{3}, 2$

Step 7

Use each root to create test intervals.

$x < - \frac{1}{3}$

$- \frac{1}{3} < x < 2$

$x > 2$

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 $x < - \frac{1}{3}$ to see if it makes the inequality true.

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Step 8.1.1

Choose a value on the interval $x < - \frac{1}{3}$ and see if this value makes the original inequality true.

$x = - 3$

Step 8.1.2

Replace $x$ with $- 3$ in the original inequality.

$3 {(- 3)}^{2} - 5 \cdot - 3 - 2 < 0$

Step 8.1.3

The left side $40$ 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 $- \frac{1}{3} < x < 2$ to see if it makes the inequality true.

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Step 8.2.1

Choose a value on the interval $- \frac{1}{3} < x < 2$ and see if this value makes the original inequality true.

$x = 0$

Step 8.2.2

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

$3 {(0)}^{2} - 5 \cdot 0 - 2 < 0$

Step 8.2.3

The left side $- 2$ 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 $x > 2$ to see if it makes the inequality true.

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Step 8.3.1

Choose a value on the interval $x > 2$ and see if this value makes the original inequality true.

$x = 4$

Step 8.3.2

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

$3 {(4)}^{2} - 5 \cdot 4 - 2 < 0$

Step 8.3.3

The left side $26$ 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.

$x < - \frac{1}{3}$ False

$- \frac{1}{3} < x < 2$ True

$x > 2$ False

$x < - \frac{1}{3}$ False

$- \frac{1}{3} < x < 2$ True

$x > 2$ False

Step 9

The solution consists of all of the true intervals.

$- \frac{1}{3} < x < 2$

Step 10

Convert the inequality to interval notation.

$(- \frac{1}{3}, 2)$

Step 11