Roots Relations Ec7846
1. **Problem statement:**
We have two quadratic equations:
- Equation 1: $x^2 + mx + 15 = 0$ with roots $\alpha$ and $\beta$.
- Equation 2: $x^2 + hx + k = 0$ with roots $\frac{\alpha}{\beta}$ and $\frac{\beta}{\alpha}$.
We need to find:
(a) The value of $k$.
(b) An expression for $h$ in terms of $m$.
2. **Recall the relationships for roots of a quadratic equation:**
For an equation $x^2 + px + q = 0$ with roots $r_1$ and $r_2$:
- Sum of roots: $r_1 + r_2 = -p$
- Product of roots: $r_1 r_2 = q$
3. **Apply these to the first equation:**
- Sum: $\alpha + \beta = -m$
- Product: $\alpha \beta = 15$
4. **For the second equation, roots are $\frac{\alpha}{\beta}$ and $\frac{\beta}{\alpha}$:**
- Sum of roots:
$$\frac{\alpha}{\beta} + \frac{\beta}{\alpha} = \frac{\alpha^2 + \beta^2}{\alpha \beta}$$
- Product of roots:
$$\frac{\alpha}{\beta} \times \frac{\beta}{\alpha} = 1$$
5. **Find $k$ (product of roots of second equation):**
Since product of roots equals $k$, we have:
$$k = 1$$
6. **Find $h$ (negative sum of roots of second equation):**
First, express $\alpha^2 + \beta^2$ in terms of $m$ and known values:
$$\alpha^2 + \beta^2 = (\alpha + \beta)^2 - 2\alpha\beta = (-m)^2 - 2 \times 15 = m^2 - 30$$
Sum of roots of second equation:
$$\frac{\alpha^2 + \beta^2}{\alpha \beta} = \frac{m^2 - 30}{15}$$
Therefore,
$$h = - \text{(sum of roots)} = - \frac{m^2 - 30}{15} = \frac{30 - m^2}{15}$$
**Final answers:**
- (a) $k = 1$
- (b) $h = \frac{30 - m^2}{15}$