Q.

The function f(x)=xx2-6x-16, x∈R-{-2,8}            [2024]

1 decreases in (-2,8) and increases in (-∞,-2)∪(8,∞)  
2 decreases in (-∞,-2) and increases in (8,∞)  
3 increases in (-∞,-2)∪(-2,8)∪(8,∞)  
4 decreases in (-∞,-2)∪(-2,8)∪(8,∞)  

Ans.

(4)

f(x)=xx2-6x-16

⇒f'(x)=(x2-6x-16)(1)-x(2x-6)(x2-6x-16)2

=-x2-16(x2-6x-16)2<0 ∀ x

∴   f(x) is a decreasing function in its domain.

⇒ f(x) decreases in (-∞,-2)∪(-2,8)∪(8,∞)