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If both roots of the quadratic equation `x^(2)+x+p=0` exceed p where `p epsilon R`, then p must lie in the interval

A

`(-oo,1)`

B

`(-oo,2)`

C

`(-oo,-2)uu(0,1//4)`

D

`(-2,1)`

Text Solution

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The correct Answer is:
To solve the problem, we need to analyze the quadratic equation \( x^2 + x + p = 0 \) and find the conditions under which both roots exceed \( p \). ### Step-by-Step Solution: 1. **Identify the Quadratic Equation**: The given quadratic equation is: \[ x^2 + x + p = 0 \] 2. **Condition for Real Roots**: For the quadratic equation to have real roots, the discriminant must be greater than zero. The discriminant \( D \) is given by: \[ D = b^2 - 4ac \] Here, \( a = 1 \), \( b = 1 \), and \( c = p \). Thus, \[ D = 1^2 - 4 \cdot 1 \cdot p = 1 - 4p \] We need \( D > 0 \): \[ 1 - 4p > 0 \] Rearranging gives: \[ 4p < 1 \quad \Rightarrow \quad p < \frac{1}{4} \] 3. **Condition for Roots Exceeding \( p \)**: Let the roots of the equation be \( r_1 \) and \( r_2 \). For both roots to exceed \( p \), we can use Vieta's formulas: - The sum of the roots \( r_1 + r_2 = -b = -1 \) - The product of the roots \( r_1 r_2 = c = p \) Since both roots exceed \( p \), we can express this condition as: \[ f(p) = p^2 + p + p > 0 \] Simplifying gives: \[ p^2 + 2p > 0 \] Factoring out \( p \): \[ p(p + 2) > 0 \] 4. **Finding the Intervals**: The inequality \( p(p + 2) > 0 \) holds when: - \( p < -2 \) or \( p > 0 \) 5. **Combining Conditions**: We have two conditions: - From the discriminant: \( p < \frac{1}{4} \) - From the roots exceeding \( p \): \( p < -2 \) or \( p > 0 \) We need to find the intersection of these intervals: - For \( p < -2 \), it is valid since \( -2 < \frac{1}{4} \). - For \( p > 0 \), it does not satisfy \( p < \frac{1}{4} \). Thus, the only valid interval for \( p \) is: \[ p \in (-\infty, -2) \cup (0, \frac{1}{4}) \] ### Final Answer: The values of \( p \) must lie in the interval: \[ p \in (-\infty, -2) \cup (0, \frac{1}{4}) \]
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