Final answer:
The alias frequency of the discrete signal is 8 Hz when a 20Hz sine wave is sampled at 12 Hz.
Step-by-step explanation:
When a sine wave is sampled at a lower frequency, the resulting discrete signal can have an alias frequency. In this case, a 20Hz sine wave is sampled at 12 Hz. To calculate the alias frequency, we can use the formula:
Alias frequency = |Sample rate - Sine wave frequency|
Substituting the given values:
Alias frequency = |12 Hz - 20 Hz| = 8 Hz
Therefore, the alias frequency of the discrete signal is 8 Hz.