For the Function \(f(x)=\tan x-4x,\ x\in\left(0,\frac{\pi}{2}\right)\), which of the following statements are correct?
A. \(f(x)\) is increasing in \(\left(0,\frac{\pi}{3}\right)\)
B. \(f(x)\) is increasing in \(\left(\frac{\pi}{3},\frac{\pi}{2}\right)\)
C. \(f(x)\) is decreasing in \(\left(0,\frac{\pi}{3}\right)\)
D. \(f(x)\) is decreasing in \(\left(\frac{\pi}{3},\frac{\pi}{2}\right)\)
Choose the correct answer from the options given below: