Practicing Success
The function $f(x)=2\log (x-2)-x^2+4x+1$ increases on the interval: |
(1, 2) (-∞ ,1) ∪ (2, 3) $(\frac{5}{2},3)$ (2, 4) |
(-∞ ,1) ∪ (2, 3) |
$f(x)=2\log (x-2)-x^2+4x+1$ $⇒f'(x)=\frac{2}{x-2}-2x+4⇒f'(x)=2[\frac{1-(x-2)^2}{x-2}]=-2\frac{(x-1)(x-3)}{x-2}$ $⇒f'(x)=\frac{2(x-1)(x-3)(x-2)}{(x-2)^2}$ $∴f'(x)>0⇒-2(x-1)(x-3)(x-2)>0$ $⇒(x-1)(x-3)(x-2)<0$ $⇒x∈(-∞ ,1) ∪ (2, 3) $ Thus, f (x) is increasing on (-∞ ,1) ∪ (2, 3) |