NTA Abhyas JEE Main2020MathematicsApplication of DerivativesPractice
The possible value of the ordered triplet a , b , c such that the function f x = x 3 + a x 2 + b x + c is a monotonic function is
Options
- A2,1 , 3
- B1 , - 1,3
- C2,2 , 4
- D2 , - 2,1
Correct answer
C. 2,2 , 4
Step-by-step solution
f x = x 3 + a x 2 + b x + c f ' x = 3 x 2 + 2 a x + b ≥ 0 ,   ∀ x ∈ R D ≤ 0 4 a 2 - 12 b ≤ 0 a 2 ≤ 3 b From the given options, 2, 2 , 4 satisfies the above condition