What is the smallest frequency that can be used to sample each of the following continuous-time signals such that the signal can be recovered from the discrete samples?
(a) \(x(t)=1+cos(2000\pi t)+cos(4000\pi t)\)
(b) \(x(t)=sin(4000\pi t)/\pi t\)
(c) \(x(t)=((sin(4000\pi t)/(\pi t))*cos(2000\pi t)\)