Quadratic Roots Cdd04B
1. **Problem statement:** Determine the condition on $k$ such that the quadratic equation $kx^2 + 3x + 6 = 0$ has two unique real roots.
2. **Formula used:** For a quadratic equation $ax^2 + bx + c = 0$, the discriminant $\Delta$ is given by:
$$\Delta = b^2 - 4ac$$
3. **Important rule:**
- If $\Delta > 0$, the equation has two distinct real roots.
- If $\Delta = 0$, the equation has exactly one real root (a repeated root).
- If $\Delta < 0$, the equation has no real roots (complex roots).
4. **Apply to given equation:** Here, $a = k$, $b = 3$, and $c = 6$.
Calculate the discriminant:
$$\Delta = 3^2 - 4 \times k \times 6 = 9 - 24k$$
5. **Condition for two unique real roots:**
$$\Delta > 0 \implies 9 - 24k > 0$$
6. **Solve inequality:**
$$9 > 24k$$
$$k < \frac{9}{24} = \frac{3}{8}$$
7. **Final answer:** The quadratic equation $kx^2 + 3x + 6 = 0$ has two unique real roots if and only if
$$k < \frac{3}{8}$$