Let the set of all values of p in mathbbR , for which both the roots of the equation x^2 - (p + 2)x + (2p + 9) = 0 are negative real numbers, be the interval (alpha, beta] . Then beta - 2alpha is equal to

Solution & Explanation

### Related Formula For both roots of a quadratic equation ax^2 + bx + c = 0 to be negative real numbers, three mandatory rules must be met simultaneously: 1. D ge 0 (Real roots) 2. Sum of roots = -b/a < 0 3. Product of roots = c/a > 0 ### Core Logic From the given quadratic equation x^2 - (p + 2)x + (2p + 9) = 0: **Condition 1**: Discriminant D ge 0 D = [-(p + 2)]^2 - 4(1)(2p + 9) ge 0 p^2 + 4p + 4 - 8p - 36 ge 0 implies p^2 - 4p - 32 ge 0 (p - 8)(p + 4) ge 0 implies p in (-infty, -4] cup [8, infty) quad dots (i) ### Step 1: Evaluate Sum and Product Conditions
Location of Roots diagram for Q64 - JEE Main 2025 Morning
Location of Roots diagram for Q64 - JEE Main 2025 Morning
**Condition 2**: Sum of roots < 0 alpha + beta = p + 2 < 0 implies p < -2 quad dots (ii) **Condition 3**: Product of roots > 0 alphabeta = 2p + 9 > 0 implies p > -frac92 quad dots (iii) ### Step 2: Find Intersection Domain Take the operational intersection across all three parameters: (i), (ii), and (iii): - From (ii) and (iii): p in left(-frac92, -2right) - Intersecting this with (i) limits the range cleanly to: p in left(-frac92, -4right] Thus, alpha = -frac92 and beta = -4. ### Step 3: Final Value Calculation Calculate the requested target expression: beta - 2alpha = -4 - 2left(-frac92right) = -4 + 9 = 5 ### Pattern Recognition Remember that if roots are strictly real and matching signs, managing product rules before analyzing spatial configurations saves major compute overhead during intersection evaluation. ### Evaluation Rubric / Model Answer null ### Chapter Mix Class 11 Mathematics: Complex Numbers and Quadratic Equations

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Q20 jee_main_2024_31_jan_morning Sign of Quadratic Expressions
Let S be the set of positive integral values of a for which fracax^2 + 2(a + 1)x + 9a + 4x^2 - 8x + 32 < 0, forall x in mathbbR. Then, the number of elements in S is:
  • A. 1
  • B. 0
  • C. infty
  • D. 3

Solution

### Core Logic For the denominator x^2 - 8x + 32, D = 64 - 128 < 0 and a = 1 > 0. Thus, x^2 - 8x + 32 > 0 forall x in mathbbR. ### Step 1: Constraint on Numerator Since the denominator is always positive, the numerator must be strictly negative for all x in mathbbR. ax^2 + 2(a + 1)x + 9a + 4 < 0 quad forall x in mathbbR This requires a < 0 and D < 0. ### Step 2: Conclusion Since a must be strictly less than 0, there are no *positive* integral values of a that satisfy the condition. Hence, S is an empty set. Number of elements is 0. ### Evaluation Rubric / Model Answer null ### Chapter Mix Class 11 Maths: Quadratic Equations

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