1. Two sine signals with the same frequency are added. Although their amplitudes and phases are different, the result of addition is still a sinusoidal signal with the original frequency.

2. If the frequency of a sinusoidal signal is equal to an integer multiple of the frequency f of another sinusoidal signal, that is, f 1 = NF, its synthesized signal is a non-sinusoidal periodic signal, and its period is equal to the period T= 1/f of the fundamental wave (the sinusoidal signal with the above frequency f is called the fundamental wave), that is, the synthesized signal is a non-sinusoidal signal with the same frequency as the fundamental wave.

3. The differential and integral of sine signal to time are still sine signals with the same frequency.

These advantages bring a lot of convenience to operation, so sinusoidal signals are widely used as typical signals or test signals in practice.