Let (2,3) be the largest open interval in which the function f(x)=2 e(x-2)-x2+ax+1 is strictly increasing and (b,c) be the largest open interval, in which the function g(x)=(x-1)3(x+2-a)2 is strictly decreasing. Then 100(a+b-c) is equal to :
- 360
- 420
- 160
- 280
Answer
(1) 360
Solution
For x>2: f'(x)= 2x-2-2x+a and f''<0 f' falls, so the largest interval ends where f'=0:
f'(3)=0 2-6+a=0 a=4
g'(x)=(x-1)2(x-2)(5x-8) — sign of g':
[figure]
g'<0 on ( 85,2 ) b= 85, c=2
100(a+b-c)=100 (4+ 85-2 )=360
Answer: (1)