JEE Main20198 Apr 2019Morning ShiftMathematicsApplication of DerivativesActual
Let f : 0 , 2 → R be a twice differentiable function such that f ' ' x > 0 , for all x ∈ 0 , 2 . If ϕ x = f x + f 2 – x , then ϕ is
Options
- Adecreasing on 0,2
- Bincreasing on 0,2
- Cincreasing on ( 0,1 ) and decreasing on 1,2
- Ddecreasing on 0,1 and increasing on ( 1,2 )
Correct answer
D. decreasing on 0,1 and increasing on ( 1,2 )
Step-by-step solution
f x : 0,2 → R and f ' ' x >   0   for x ∈   [ 0,2 ] ⇒ f ' ( x ) is increasing for x ∈   [ 0,2 ] Now, ϕ ( x ) = f ( x ) + f ( 2 - x ) ⇒ ϕ ' x = f ' x - f ' ( 2 - x ) For   x ∈   [ 0,1 ) , x   <   2   –   x ⇒ f ' ( x ) < f ' ( 2 - x ) ⇒ ϕ ' ( x ) < 0 For x ∈   ( 1 ,   2 ] , x   >   2   –   x ⇒ f &#