Find Mn
1. **State the problem:** We have two quadratic equations:
- Equation 1: $2x^2 - mx + 8 = 0$ with roots $\alpha$ and $\beta$.
- Equation 2: $5x^2 - 10x + 5n = 0$ with roots $\frac{1}{\alpha}$ and $\frac{1}{\beta}$.
We need to find the product $mn$.
2. **Use sum and product of roots for the first equation:**
For quadratic equation $ax^2 + bx + c = 0$ with roots $r_1$ and $r_2$, sum of roots $= -\frac{b}{a}$ and product of roots $= \frac{c}{a}$.
From the first equation:
Sum: $\alpha + \beta = \frac{m}{2}$ (since $-(-m)/2 = m/2$)
Product: $\alpha \beta = \frac{8}{2} = 4$
3. **Use sum and product of roots for the second equation:**
Equation: $5x^2 - 10x + 5n = 0$.
Sum of roots $= -\frac{-10}{5} = 2$.
Product of roots $= \frac{5n}{5} = n$.
Given roots are $\frac{1}{\alpha}$ and $\frac{1}{\beta}$:
Sum: $\frac{1}{\alpha} + \frac{1}{\beta} = 2$
Product: $\frac{1}{\alpha} \cdot \frac{1}{\beta} = n$
4. **Express sum and product of reciprocals in terms of $\alpha$ and $\beta$:**
Sum of reciprocals:
$$\frac{1}{\alpha} + \frac{1}{\beta} = \frac{\alpha + \beta}{\alpha \beta} = \frac{m/2}{4} = \frac{m}{8}$$
Given this sum equals 2:
$$\frac{m}{8} = 2 \Rightarrow m = 16$$
5. **Find product of reciprocals:**
$$n = \frac{1}{\alpha \beta} = \frac{1}{4}$$
6. **Calculate $mn$:**
$$mn = 16 \times \frac{1}{4} = 4$$
**Final answer:**
$\boxed{4}$