The function \(f\), where \(f(x) = a \sin x + b\), is defined for the domain \(0 \leq x \leq 2\pi\). Given that \(f\left(\frac{1}{2}\pi\right) = 2\) and that \(f\left(\frac{3}{2}\pi\right) = -8\),

(i) find the values of \(a\) and \(b\),

(ii) find the values of \(x\) for which \(f(x) = 0\), giving your answers in radians correct to 2 decimal places,

(iii) sketch the graph of \(y = f(x)\).