If \(f(x)=\sin x-\cos x,\ x\in[0,2\pi]\) then (A) \(f(x)\) is increasing in \(\left(0,\frac{3\pi}{4}\right)\) (B) \(f(x)\) is decreasing in \(\left(0,\frac{3\pi}{4}\right)\) (C) \(f(x)\) is decreasing in \(\left(\frac{3\pi}{4},\frac{7\pi}{4}\right)\) (D) \(f(x)\) is decreasing in \(\left(\frac{7\pi}{4},2\pi\right)\) Choose the correct answer from the options given below: