Voltage of an Electrical Circuit The voltage $E$ in an electrical circuit is modeled by
$$E=5 \cos 120 \pi t$$ where $t$ is time measured in seconds.
(a) Find the amplitude and the period.
(b) Find the frequency.
(c) Find $E,$ to the nearest thousandth, when $t=0,0.03,0.06,0.09,0.12$
(d) Graph $E$ for $0 \leq t \leq \frac{1}{30}$