Estimation of Fourier Coefficients of a Periodic Signal 
A sine wave whose frequency is some integer multiple of a fundamental sine wave is called,
What is he duty cycle of a square wave with equal durations positive and negative alterations?
What is the frequency of the 7th harmonic of a 2KHz sine wave?
What is the peak value of 5th harmonic if the square wave has a peak voltage of 3V and a frequency of 48KHz?
Which instrument produces frequency domain information?