Question

What is output signal when a signal x(t)=cos(2*pi*40*t) is sampled with a sampling frequency of 20Hz?

(a) cos(pi*n)

(b) cos(2*pi*n)

(c) cos(4*pi*n)

(d) cos(8*pi*n)

I have been asked this question in an online quiz.

I'd like to ask this question from A2D and D2A Converters in chapter DSP – Basic Signaling of Digital Signal Processing

Answer 1

Correct answer is (c) cos(4*pi*n)

Explanation: From the question F=40Hz, Fs=20Hz

=>f=F/Fs

=>f=40/20

=>f=2Hz

=>x(n)=cos(4*pi*n).