The function f(x) = 2log(x - 2) - x2 + 4x + 1 increases on the interval |
(1, 2) (2, 3) (1, 3) (2, 4) |
(2, 3) |
Clearly, f(x) is defined for all x > 2. We have, $f(x)=2 \log (x-2)-x^2+4 x+1 $ $\Rightarrow f'(x)=\frac{2}{x-2}-2 x+4 $ $\Rightarrow f'(x)=2\left\{\frac{1-(x-2)^2}{x-2}\right\}=-\frac{2(x-1)(x-3)}{x-2} $ $\Rightarrow f'(x)=-\frac{2(x-1)(x-3)(x-2)}{(x-2)^2} $ ∴ $f'(x)>0 $ $\Rightarrow -2(x-1)(x-3)(x-2)>0$ $\Rightarrow (x-1)(x-2)(x-3)<0 \Rightarrow x \in(-\infty, 1) \cup(2,3)$ Clearly, domain of $f(x)$ is $(2, \infty)$. Thus, $f(x)$ is increasing on $(2,3)$. |