NTA Abhyas JEE Main2020MathematicsQuadratic EquationPractice
If the graph of the function y = a - b 2 x 2 + 2 a + b - 2 c x + 1   ∀ a ≠ b is strictly above the x -axis, then
Options
- Aa < b < c
- Ba < c < b
- Cb < a < c
- Dc < b < a
Correct answer
B. a < c < b
Step-by-step solution
D = B 2 - 4 A C = 2 a + b - 2 c 2 - 4 a - b 2 = 4 a + b - 2 c 2 - a - b 2 = 4 a + b - 2 c - a + b a + b - 2 c + a - b = 4 2 b - 2 c 2 a - 2 c = 16 b - c a - c = 16 c - b c - a If c lies between a and b , then D is negative. Hence, the roots will be imaginary and the graph will be entirely above the x -axis as the coefficient of x 2 is positive.