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Quadratic Equations appeared 26 times across 3 years — 3% of Mathematics. This question is from Roots of Quadratic Equation.

Year 2026 2025 2024 Total
Questions 11 10 5 26

Let a, b, c be the length of three sides of a triangle satisfying the condition (a² + b²)x² - 2b(a + c)x + (b² + c²) = 0. If the set of all possible values of x is the interval (α, β) then 12(α² + β²) is equal to

Numerical Answer Type:
Enter a numerical value Answer: 36 to 36 +4 marks

Solution & Explanation

Core Logic

Given equation: (a²+b²)x² - 2b(a+c)x + b²+c² = 0. Expand and rearrange into perfect squares:

(a²x² - 2abx + b²) + (b²x² - 2bcx + c²) = 0 (ax - b)² + (bx - c)² = 0

Since squares must be non-negative, each term is zero:

ax - b = 0 x = (b)/(a) bx - c = 0 x = (c)/(b)

Thus, b = ax and c = bx = ax². Since a,b,c form a triangle, the triangle inequality holds:

  • a + b > c a + ax > ax² x² - x - 1 < 0 1-√(5)2 < x < 1+√(5)2
  • a + c > b a + ax² > ax x² - x + 1 > 0 (Always true for real x)
  • b + c > a ax + ax² > a x² + x - 1 > 0 x > -1+√(5)2 or x < -1-√(5)2.
  • Taking the intersection (and noting x > 0 since sides are positive):

√(5)-12 < x < √(5)+12

So, α = √(5)-12 and β = √(5)+12. Calculate 12(α² + β²):

12 ( 6-2√(5)4 + 6+2√(5)4 ) = 12 ( (12)/(4) ) = 36
Chapter Mix

Class 11 Maths: Complex Numbers and Quadratic Equations Class 11 Maths: Straight Lines

Reference Study Guides

More Quadratic Equations Previous-Year Questions — Page 6

Q20 jee_main_2024_31_jan_morning Sign of Quadratic Expressions
Let S be the set of positive integral values of a for which (ax² + 2(a + 1)x + 9a + 4)/(x² - 8x + 32) < 0, x in R. Then, the number of elements in S is:
  • A. 1
  • B. 0
  • C. ∞
  • D. 3

Solution

Core Logic

For the denominator x² - 8x + 32, D = 64 - 128 < 0 and a = 1 > 0. Thus, x² - 8x + 32 > 0 x in R.

Step 1: Constraint on Numerator

Since the denominator is always positive, the numerator must be strictly negative for all x in R.

ax² + 2(a + 1)x + 9a + 4 < 0 x in R

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.

Chapter Mix

Class 11 Maths: Quadratic Equations

More Quadratic Equations Questions — jee_main_2024_31_jan_evening

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