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 ≤ - 5 or x ≥ - 2 }
To solve the quadratic inequality algebraically, we will follow three steps.
Substitute values
Calculate root
| x=- 7 ± 3/2 | |
|---|---|
| x=- 7 + 3/2 | x=- 7 - 3/2 |
| x=- 7/2+3/2 | x=- 7/2-3/2 |
| x= - 2 | x= - 5 |
The solutions of the related equation are - 2 and - 5. Let's plot them on a number line. Since the original is not a strict inequality, the points will be closed.
x= - 10
Calculate power
a(- b)=- a * b
Subtract terms
| Interval | Test Value | Statement | Is It Part of the Solution? |
|---|---|---|---|
| - 5 ≤ x ≤ - 2 | - 3 | - 12 ≱ - 10 * | No |
| x ≥ - 2 | 0 | 0 ≥ - 10 ✓ | Yes |
We can now write the solution set and show it on a number line. { x| x ≤ - 5 or x ≥ - 2 } or (- ∞, - 5] ⋃ [- 2, ∞)