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If p ad q are non-zero constants, the eq...

If p ad q are non-zero constants, the equation `x^(2)+px+q=0` has roots `alpha and beta`, then the equation `qx^(2)+px+1=0` has roots

A

`alpha and 1//beta`

B

`1//alpha and beta`

C

`1//alpha and 1//beta`

D

none of these

Text Solution

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The correct Answer is:
To solve the problem, we need to analyze the two quadratic equations given and their roots. Let's break it down step by step. ### Step 1: Identify the roots of the first equation The first equation is given as: \[ x^2 + px + q = 0 \] Let the roots of this equation be \( \alpha \) and \( \beta \). Using Vieta's formulas, we know: - The sum of the roots \( \alpha + \beta = -\frac{p}{1} = -p \) - The product of the roots \( \alpha \beta = \frac{q}{1} = q \) ### Step 2: Analyze the second equation The second equation is: \[ qx^2 + px + 1 = 0 \] We need to find the roots of this equation, which we will denote as \( \alpha_1 \) and \( \beta_1 \). Again, applying Vieta's formulas for this equation: - The sum of the roots \( \alpha_1 + \beta_1 = -\frac{p}{q} \) - The product of the roots \( \alpha_1 \beta_1 = \frac{1}{q} \) ### Step 3: Relate the roots of the second equation to the first We need to find roots \( \alpha_1 \) and \( \beta_1 \) such that: 1. Their sum \( \alpha_1 + \beta_1 = -\frac{p}{q} \) 2. Their product \( \alpha_1 \beta_1 = \frac{1}{q} \) ### Step 4: Check possible forms for \( \alpha_1 \) and \( \beta_1 \) We can express the roots \( \alpha_1 \) and \( \beta_1 \) in terms of \( \alpha \) and \( \beta \). A common transformation is to take the reciprocals of the roots of the first equation: \[ \alpha_1 = \frac{1}{\alpha}, \quad \beta_1 = \frac{1}{\beta} \] ### Step 5: Verify the sum and product Now, we calculate the sum and product of \( \alpha_1 \) and \( \beta_1 \): - The sum: \[ \alpha_1 + \beta_1 = \frac{1}{\alpha} + \frac{1}{\beta} = \frac{\beta + \alpha}{\alpha \beta} = \frac{-p}{q} \] - The product: \[ \alpha_1 \beta_1 = \frac{1}{\alpha} \cdot \frac{1}{\beta} = \frac{1}{\alpha \beta} = \frac{1}{q} \] Both conditions are satisfied. ### Conclusion Thus, the roots \( \alpha_1 \) and \( \beta_1 \) of the equation \( qx^2 + px + 1 = 0 \) are: \[ \alpha_1 = \frac{1}{\alpha}, \quad \beta_1 = \frac{1}{\beta} \]
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ML KHANNA-THEORY OF QUADRATIC EQUATIONS -Self Assessment Test
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