Given that $\alpha$ and $\beta$ are the roots of the quadratic equation $x^2 + 2x - 4 = 0$, we need to find the quadratic equation whose roots are $\frac{3}{\beta}$ and $\frac{3}{\alpha}$.

AlgebraQuadratic EquationsRoots of EquationVieta's Formulas
2025/3/10

1. Problem Description

Given that α\alpha and β\beta are the roots of the quadratic equation x2+2x4=0x^2 + 2x - 4 = 0, we need to find the quadratic equation whose roots are 3β\frac{3}{\beta} and 3α\frac{3}{\alpha}.

2. Solution Steps

First, we find the sum and product of the roots of the given equation x2+2x4=0x^2 + 2x - 4 = 0.
The sum of the roots is α+β=21=2\alpha + \beta = -\frac{2}{1} = -2.
The product of the roots is αβ=41=4\alpha \beta = \frac{-4}{1} = -4.
Now, we want to find the equation whose roots are 3β\frac{3}{\beta} and 3α\frac{3}{\alpha}.
The sum of the new roots is 3β+3α=3(1β+1α)=3(α+βαβ)=3(24)=3(12)=32\frac{3}{\beta} + \frac{3}{\alpha} = 3(\frac{1}{\beta} + \frac{1}{\alpha}) = 3(\frac{\alpha + \beta}{\alpha \beta}) = 3(\frac{-2}{-4}) = 3(\frac{1}{2}) = \frac{3}{2}.
The product of the new roots is 3β3α=9αβ=94=94\frac{3}{\beta} \cdot \frac{3}{\alpha} = \frac{9}{\alpha \beta} = \frac{9}{-4} = -\frac{9}{4}.
A quadratic equation with roots r1r_1 and r2r_2 can be written as x2(r1+r2)x+r1r2=0x^2 - (r_1 + r_2)x + r_1 r_2 = 0.
Therefore, the equation with roots 3β\frac{3}{\beta} and 3α\frac{3}{\alpha} is given by
x2(32)x+(94)=0x^2 - (\frac{3}{2})x + (-\frac{9}{4}) = 0
x232x94=0x^2 - \frac{3}{2}x - \frac{9}{4} = 0
Multiplying by 4 to eliminate fractions, we get
4x26x9=04x^2 - 6x - 9 = 0

3. Final Answer

4x26x9=04x^2 - 6x - 9 = 0

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