21. The voltage, V, in volts, of a power supply can be modeled by the function v(t) = 150cos(2t) + 20 v(t) = 150 cos 2t + 20, where t is the time, in seconds. a) State the value of the period, in seconds. b) State the frequency, in Hertz (Hz) c) Find the maximum and minimum voltages, and all the times at which they occur on the interval [0,2].