The function \(\mathrm{f}\) is given by

\(\mathrm{f}(x)=2\cos\frac{x}{3}-1.\)

(a) Write down the amplitude of \(\mathrm{f}\).

(b) Write down the period of \(\mathrm{f}\).

(c) Sketch the graph of \(y=\mathrm{f}(x)\) for \(-\pi\leq x\leq3\pi\).