Ques. 1JEE Main 2024, 29 January (Evening Shift)
The function f(x)= xx2-6x-16, x R-\-2,8\
- decreases in (- ,-2) (-2,8) (8, )
- increases in (- ,-2) (-2,8) (8, )
- decreases in (-2,8) and increases in (- ,-2) (8, )
- decreases in (- ,-2) and increases in (8, )
Answer
(1) decreases in (- ,-2) (-2,8) (8, )
Solution
f'(x)= (x2-6x-16) 1-x(2x-6)(x2-6x-16)2
= -(x2+16)(x2-6x-16)2
∵ x2+16>0 and the denominator is a square ⇒ f'(x)<0 for every x -2,8
f decreases in each of (- ,-2),(-2,8),(8, )
Answer: (1)