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If (alpha) and(beta) be the roots of the...

If (alpha) and(beta) be the roots of the equation `ax^2+bx + c=0`, find the value of
`(alpha^(2))/(beta) + (beta^(2))/(alpha)`

A

`(ab-b^(2)c)/(2b^(2)c)`

B

`(3bc -a^(3))/(b^(2)c)`

C

`(3ac -b^(2))/(a^(2)c)`

D

`(3abc-b^(3))/(a^(2)c)`

Text Solution

AI Generated Solution

The correct Answer is:
To solve the problem, we need to find the value of \(\frac{\alpha^2}{\beta} + \frac{\beta^2}{\alpha}\) where \(\alpha\) and \(\beta\) are the roots of the quadratic equation \(ax^2 + bx + c = 0\). ### Step-by-step Solution: 1. **Use Vieta's Formulas**: From Vieta's formulas, we know that: - \(\alpha + \beta = -\frac{b}{a}\) (sum of roots) - \(\alpha \beta = \frac{c}{a}\) (product of roots) 2. **Rewrite the Expression**: We need to simplify the expression \(\frac{\alpha^2}{\beta} + \frac{\beta^2}{\alpha}\). We can rewrite it as: \[ \frac{\alpha^2}{\beta} + \frac{\beta^2}{\alpha} = \frac{\alpha^3 + \beta^3}{\alpha \beta} \] 3. **Use the Identity for Sum of Cubes**: The sum of cubes can be expressed as: \[ \alpha^3 + \beta^3 = (\alpha + \beta)(\alpha^2 - \alpha\beta + \beta^2) \] We can also express \(\alpha^2 + \beta^2\) using the identity: \[ \alpha^2 + \beta^2 = (\alpha + \beta)^2 - 2\alpha\beta \] Thus, \[ \alpha^3 + \beta^3 = (\alpha + \beta)((\alpha + \beta)^2 - 3\alpha\beta) \] 4. **Substitute Vieta's Values**: Now substituting the values from Vieta's formulas: \[ \alpha^3 + \beta^3 = \left(-\frac{b}{a}\right)\left(\left(-\frac{b}{a}\right)^2 - 3\frac{c}{a}\right) \] Simplifying this gives: \[ = -\frac{b}{a}\left(\frac{b^2}{a^2} - \frac{3c}{a}\right) = -\frac{b}{a}\left(\frac{b^2 - 3ac}{a^2}\right) = -\frac{b(b^2 - 3ac)}{a^3} \] 5. **Combine Everything**: Now substituting back into our expression: \[ \frac{\alpha^3 + \beta^3}{\alpha \beta} = \frac{-\frac{b(b^2 - 3ac)}{a^3}}{\frac{c}{a}} = -\frac{b(b^2 - 3ac)}{ac} \] 6. **Final Expression**: Thus, we have: \[ \frac{\alpha^2}{\beta} + \frac{\beta^2}{\alpha} = \frac{3ac - b^2}{ac} \] ### Conclusion: The final value of \(\frac{\alpha^2}{\beta} + \frac{\beta^2}{\alpha}\) is: \[ \frac{3ac - b^2}{ac} \]
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