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 ≤ - 3.91 or x≥ 1.41 }
To solve the quadratic inequality algebraically, we will follow three steps.
Substitute values
| x=- 5±sqrt(113)/4 | |
|---|---|
| x=- 5 + sqrt(113)/4 | x=- 5 - sqrt(113)/4 |
| x=- 5/4+sqrt(113)/4 | x=- 5/4-sqrt(113)/4 |
| x≈ 1.41 | x≈ - 3.91 |
The solutions of the related equation are approximately - 3.91 and 1.41. 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? |
|---|---|---|---|
| - 3.91 ≤ x ≤ 1.41 | 0 | - 11 ≱ 0 * | No |
| x ≥ 1.41 | 1 | - 11 ≥ - 18 ✓ | Yes |
We can now write the solution set and show it on a number line. { x| x ≤ - 3.91 or x≥ 1.41 } or (- ∞, - 3.91] ⋃ [1.41, ∞)