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| x ≤ - 2.75 or x≥ 1 }
To solve the quadratic inequality algebraically, we will follow three steps.
Substitute values
Calculate root
| x=7 ± 15/- 8 | |
|---|---|
| x=7 + 15/- 8 | x=7 -15/- 8 |
| x=- 7/8-15/8 | x=- 7/8+15/8 |
| x=- 2.75 | x=1 |
The solutions of the related equation are - 2.75 and 1. Let's plot them on a number line. Since the original is not a strict inequality, the points will be closed.
| Interval | Test Value | Statement | Is It Part of the Solution? |
|---|---|---|---|
| - 2.75 ≤ x ≤ 1 | 0 | 11 ≰ 0 * | No |
| x ≥ 1 | 2 | 11 ≤ 30 ✓ | Yes |
We can now write the solution set and show it on a number line. { x| x ≤ - 2.75 or x≥ 1 } or (- ∞, - 2.75] ⋃ [1, ∞)