NTA Abhyas JEE Main2020MathematicsQuadratic EquationPractice
If - 3 < x 2 - λ x - 2 x 2 + x + 1 < 2 for all x ∈ R , then the value of λ belongs to
Options
- A- 1,7
- B- 6,2
- C- 1,2
- D- 6,7
Correct answer
C. - 1,2
Step-by-step solution
- 3 < x 2 - λ x - 2 x 2 + x + 1 < 2 ⇒ - 3 x 2 - 3 x - 3 < x 2 - λ x - 2 < 2 x 2 + 2 x + 2 since   x 2 + x + 1 > 0 ,   ∀ x ∈ R ⇒ 4 x 2 + x 3 - λ + 1 > 0 , x 2 + x 2 + λ + 4 > 0 i   4 x 2 - x λ - 3 + 1 > 0 ⇒ D < 0 ⇒ λ - 3 2 - 4 × 4 × 1 < 0 ⇒ λ - 3 + 4 λ - 3 - 4 < 0 ⇒ λ + 1 λ - 7 < 0 ⇒ λ ∈ - 1,7 i i   x 2 + x λ + 2 + 4 >