Let g(x)=3f ( x3 )+f(3-x) and f''(x)>0 for all x (0,3). If g is decreasing in (0, ) and increasing in ( ,3), then 8 is :
- 0
- 24
- 18
- 20
Answer
(3) 18
Solution
g'(x)=f' ( x3 )-f'(3-x)
∵ f''>0 f' is increasing
g'(x)<0 f' ( x3 )<f'(3-x) x3<3-x x< 94
g decreases in (0, 94 ), increases in ( 94,3 ) = 94
8 =18
Answer: (3)