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If alpha and beta be the roots of the eq...

If `alpha and beta` be the roots of the equation `x^(2) + px - 1//(2p^(2)) = 0`,
where `p in R`. Then the minimum value of `alpha^(4) + beta^(4)` is

A

`2sqrt2`

B

`2 - sqrt2`

C

`2`

D

`2 + sqrt2`

Text Solution

AI Generated Solution

The correct Answer is:
To find the minimum value of \( \alpha^4 + \beta^4 \) where \( \alpha \) and \( \beta \) are the roots of the equation \[ x^2 + px - \frac{1}{2p^2} = 0, \] we can use the properties of the roots of a quadratic equation. ### Step 1: Identify the sum and product of the roots From Vieta's formulas, for the quadratic equation \( ax^2 + bx + c = 0 \): - The sum of the roots \( \alpha + \beta = -\frac{b}{a} = -\frac{p}{1} = -p \). - The product of the roots \( \alpha \beta = \frac{c}{a} = -\frac{1}{2p^2} \). ### Step 2: Express \( \alpha^4 + \beta^4 \) in terms of \( \alpha + \beta \) and \( \alpha \beta \) We can express \( \alpha^4 + \beta^4 \) using the identity: \[ \alpha^4 + \beta^4 = (\alpha^2 + \beta^2)^2 - 2\alpha^2\beta^2. \] ### Step 3: Find \( \alpha^2 + \beta^2 \) Using the identity \( \alpha^2 + \beta^2 = (\alpha + \beta)^2 - 2\alpha\beta \): \[ \alpha^2 + \beta^2 = (-p)^2 - 2\left(-\frac{1}{2p^2}\right) = p^2 + \frac{1}{p^2}. \] ### Step 4: Find \( \alpha^2 \beta^2 \) We have: \[ \alpha^2 \beta^2 = (\alpha \beta)^2 = \left(-\frac{1}{2p^2}\right)^2 = \frac{1}{4p^4}. \] ### Step 5: Substitute back into \( \alpha^4 + \beta^4 \) Now substituting \( \alpha^2 + \beta^2 \) and \( \alpha^2 \beta^2 \) into the expression for \( \alpha^4 + \beta^4 \): \[ \alpha^4 + \beta^4 = \left(p^2 + \frac{1}{p^2}\right)^2 - 2\left(\frac{1}{4p^4}\right). \] ### Step 6: Simplify the expression Calculating \( \left(p^2 + \frac{1}{p^2}\right)^2 \): \[ \left(p^2 + \frac{1}{p^2}\right)^2 = p^4 + 2 + \frac{1}{p^4}. \] Thus, \[ \alpha^4 + \beta^4 = p^4 + 2 + \frac{1}{p^4} - \frac{1}{2p^4} = p^4 + 2 + \frac{1}{2p^4}. \] ### Step 7: Find the minimum value Let \( y = p^4 + \frac{1}{2p^4} \). To find the minimum value of \( y \), we can use the AM-GM inequality: \[ p^4 + \frac{1}{2p^4} \geq 2\sqrt{p^4 \cdot \frac{1}{2p^4}} = 2\sqrt{\frac{1}{2}} = \sqrt{2}. \] Thus, the minimum value of \( y \) is \( \sqrt{2} \) when \( p^4 = \frac{1}{2p^4} \) or \( p^8 = \frac{1}{2} \). So the minimum value of \( \alpha^4 + \beta^4 \) is: \[ \sqrt{2} + 2. \] ### Final Answer The minimum value of \( \alpha^4 + \beta^4 \) is: \[ 2 + \sqrt{2}. \]

To find the minimum value of \( \alpha^4 + \beta^4 \) where \( \alpha \) and \( \beta \) are the roots of the equation \[ x^2 + px - \frac{1}{2p^2} = 0, \] we can use the properties of the roots of a quadratic equation. ...
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