514-1 Trigonometric Fourier series Any periodic waveform f(t=f(t+n) can be expressed y a Fourier series provided that (1)If it is discontinuous, there are only a finite number of discontinuous in the period T; (2) It has a finite average value over the period t 3 )It has a finite number of positive and negative maximums in the period T.§14-1 Trigonometric Fourier series Any periodic waveform f(t)=f(t+T) can be expressed by a Fourier series provided that (2) It has a finite average value over the period T; (3) It has a finite number of positive and negative maximums in the period T. (1) If it is discontinuous, there are only a finite number of discontinuous in the period T;