The bug here is that the period is 0.07 and so is the sampling rate. To fix this, we can just try a smaller sampling rate, something like 0.001 instead.
F0 = 13; T0 = 1/F0; Ts = 0.001; t = 0:Ts:13*T0; x = real(exp(j**2*pi*F0*t-pi/2))); plot(t,x)
