1. The problem is to solve the quadratic inequality $$2x^2 \geq 7x + 15$$ in the set of real numbers.
2. First, rewrite the inequality in standard form by moving all terms to one side:
$$2x^2 - 7x - 15 \geq 0$$
3. To solve this inequality, we find the roots of the quadratic equation:
$$2x^2 - 7x - 15 = 0$$
4. Use the quadratic formula:
$$x = \frac{-b \pm \sqrt{b^2 - 4ac}}{2a}$$
where $a=2$, $b=-7$, and $c=-15$.
5. Calculate the discriminant:
$$\Delta = (-7)^2 - 4 \times 2 \times (-15) = 49 + 120 = 169$$
6. Find the roots:
$$x = \frac{-(-7) \pm \sqrt{169}}{2 \times 2} = \frac{7 \pm 13}{4}$$
7. Calculate each root:
- $$x_1 = \frac{7 - 13}{4} = \frac{-6}{4} = -\frac{3}{2}$$
- $$x_2 = \frac{7 + 13}{4} = \frac{20}{4} = 5$$
8. The quadratic opens upwards since $a=2 > 0$, so the parabola is positive outside the roots and negative between them.
9. Therefore, the solution to the inequality $$2x^2 - 7x - 15 \geq 0$$ is:
$$x \leq -\frac{3}{2} \quad \text{or} \quad x \geq 5$$
This means all real numbers less than or equal to $-\frac{3}{2}$ or greater than or equal to $5$ satisfy the inequality.
Quadratic Inequality 093A38
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