JEE Main202127 Jul 2021Evening ShiftMathematicsApplication of DerivativesActual
Let f : a , b → R be twice differentiable function such that f x = ∫ a x g t d t for a differentiable function g x . If f x = 0 has exactly five distinct roots in a , b , then g x g ' x = 0 has at least :
Options
- Atwelve roots in a , b
- Bfive roots in a , b
- Cseven roots in a , b
- Dthree roots in a , b
Correct answer
C. seven roots in a , b
Step-by-step solution
Let f : a , b → R be twice differentiable function such that f x = ∫ a x g t d t for a differentiable function g x , Now, f x = ∫ a x g t d t Since, f x has 5 roots and f ' x has atleast 4 roots g x has atleast 4 roots Therefore, g ' x has atleast 3 roots. Hence, g x g ' x has atleast 7 roots.