Digital Signal Processing Toolkit

For a signal (sin (10t) * cos (10t)), what should be the minimum sampling frequency avoid aliasing?
The average value of the signal cos x over (0, pi) is:
If the sampling frequency is specified as 15 Hz, which of the following signals would undergo aliasing?
In which of the following operations, one of the functions is reversed and shifted?
For a filter transfer function, which of the following sets of poles and zeros is acceptable?