Solve for x x^2-x-20<0

$x^{2} - x - 20 < 0$

Step 1

Convert the inequality to an equation.

$x^{2} - x - 20 = 0$

Step 2

Factor $x^{2} - x - 20$ using the AC method.

Consider the form $x^{2} + b x + c$ . Find a pair of integers whose product is $c$ and whose sum is $b$ . In this case, whose product is $- 20$ and whose sum is $- 1$ .

$- 5, 4$

Write the factored form using these integers.

$(x - 5) (x + 4) = 0$

Step 3

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

$x - 5 = 0$

$x + 4 = 0$

Step 4

Set $x - 5$ equal to $0$ and solve for $x$ .

Set $x - 5$ equal to $0$ .

$x - 5 = 0$

Add $5$ to both sides of the equation.

$x = 5$

Step 5

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

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

$x + 4 = 0$

Subtract $4$ from both sides of the equation.

$x = - 4$

Step 6

The final solution is all the values that make $(x - 5) (x + 4) = 0$ true.

$x = 5, - 4$

Step 7

Use each root to create test intervals.

$x < - 4$

$- 4 < x < 5$

$x > 5$

Step 8

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

Test a value on the interval $x < - 4$ to see if it makes the inequality true.

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

$x = - 6$

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

${(- 6)}^{2} - (- 6) - 20 < 0$

The left side $22$ is not less than the right side $0$ , which means that the given statement is false.

False

Test a value on the interval $- 4 < x < 5$ to see if it makes the inequality true.

Choose a value on the interval $- 4 < x < 5$ and see if this value makes the original inequality true.

$x = 0$

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

${(0)}^{2} - (0) - 20 < 0$

The left side $- 20$ is less than the right side $0$ , which means that the given statement is always true.

True

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

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

$x = 8$

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

${(8)}^{2} - (8) - 20 < 0$

The left side $36$ is not less than the right side $0$ , which means that the given statement is false.

False

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

$x < - 4$ False

$- 4 < x < 5$ True

$x > 5$ False

$x < - 4$ False

$- 4 < x < 5$ True

$x > 5$ False

Step 9

The solution consists of all of the true intervals.

$- 4 < x < 5$

Step 10

The result can be shown in multiple forms.

Inequality Form:

$- 4 < x < 5$

Interval Notation:

$(- 4, 5)$

Step 11

Solve for x x^2-x-20<0

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