b
(b)\(P = \frac{1}{2}{V_o}{i_o}\cos \phi \Rightarrow P = {P_{Peak}}.\cos \phi \)\( \Rightarrow \frac{1}{2}({P_{peak}}) = {P_{peak}}\cos \phi \Rightarrow \cos \phi = \frac{1}{2} \Rightarrow \phi = \frac{\pi }{3}\)