5. Quadratic Inequalities
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Solve the related quadratic equation, plot the solutions on a number line, and test a value from each interval.
{ x| - 8 < x < 2 }
To solve the quadratic inequality algebraically, we will follow three steps.
Substitute values
Calculate root
| x=- 6 ± 10/2 | |
|---|---|
| x=- 6 + 10/2 | x=- 6 - 10/2 |
| x=- 6/2 + 10/2 | x=- 6/2 - 10/2 |
| x=2 | x=- 8 |
The solutions of the related equation are - 8 and 2. Let's plot them on a number line. Since the original is a strict inequality, the points will be open.
| Interval | Test Value | Statement | Is It Part of the Solution? |
|---|---|---|---|
| - 8 < x < 2 | 0 | - 16 < 0 âś“ | Yes |
| x > 2 | 3 | 11 ≮ 0 * | No |
We can now write the solution set and show it on a number line. { x| - 8 < x < 2 } or (- 8, 2)