The sum, of the squares of all the roots of the equation x^2 + |2x - 3| - 4 = 0, is: (1) 3(3 - sqrt2) (2) 6(3 - sqrt2) (3) 6(2 - sqrt2) (4) 3(2 - sqrt2)

Solution & Explanation

### Related Formula Modulus definition rule: |x| = begincases x, & x ge 0 \\ -x, & x < 0 endcases ### Core Logic Analyze the roots by splitting into cases around the critical threshold x = frac32: **Case I:** x ge frac32 x^2 + 2x - 3 - 4 = 0 implies x^2 + 2x - 7 = 0 implies x = 2sqrt2 - 1 (We select the positive root since 2sqrt2-1 ge 1.5). ### Step 1: Evaluating the alternate domain branch **Case II:** x < frac32 x^2 - (2x - 3) - 4 = 0 implies x^2 - 2x - 1 = 0 implies x = 1 - sqrt2 (We select 1-sqrt2 since it satisfies the inequality constraint). ### Step 2: Summing the Squares of the Roots textSum of Squares = (2sqrt2 - 1)^2 + (1 - sqrt2)^2 = (8 - 4sqrt2 + 1) + (1 - 2sqrt2 + 2) = 12 - 6sqrt2 = 6(2 - sqrt2) ### Pattern Recognition Always validate absolute root values against their domain restrictions to avoid including phantom solutions. ### Evaluation Rubric / Model Answer null ### Chapter Mix Class 11 Maths: 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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