3. [Periodic signal and Fourier Series Expansion - 8 pts] Determine if the signals given below are periodic. If not, state the reason; if yes, calculate the CTFS and sketch magnitude and phase. (a) x (t)= cos(271) cos(V2rt) Periodic: Non-periodic: If applicable, show the expression of CTFS c, [k] of xj(t), graph the magnitude and phase c, [k] 0 0 (b) xz (t)= 2 + cos(at)+sin(24t) Periodic: Non-periodic: If applicable, calculate the harmonic functions [k] of x2(t), graph the magnitude and phase cx [k]. 0 0