The voltage across and current through a certain device are given by ?(t) = 5cos(4?t) V and i(t) = 0.1cos(4?t) A, respectively. Determine: (a) The instantaneous power p(t) at t = 0 and t = 0.25 s. (b) The average power pav, defined as the average value of p(t) over a full time period of the cosine function (0 to 0.5 s