Sampling theorem question

Thread Starter


Joined May 7, 2007
hello every body.

i am not sure if this is the right place or not to post my question, cuz it is not really circuit related. anw here is the question

Consider the continuous-time signal
x(t)=15 −8⋅cos(30000πt +π / 2)− 4⋅sin(50000πt −π / 4)

If the signal x(t) is passed through a lowpass filter that removes all frequency
components above 20kHz,

(ii) Write the expression for the discrete-time signal if the signal is sampled at
fs = 40kHz. [10%]

(iii) Calculate the frequency f, 0 < f < 0.5 fs , of the sinusoid that yields samples
identical to those obtained by the sampling rate of 40kHz. Comment on the
result. [15%]

for the first part i guess all wat i have to do is multiply the signal with the impulse function at time delays equal to n*1/fs. Am i on the right track????

for the ssecond part. I couldn't even understand wat is it asking for????