60 SIGNALS AND SIGNAL SPACE Figure P.2.7-4 Also, the product of an even and an odd function is an odd function, the product of two odd functions is an even function, and the product of two even functions is an even function. 2.7-4 For each of the periodic signals shown in Fig. P2.7-4, find the exponential Fourier series and sketch the amplitude and phase spectra. Note any symmetric property. (a) -7 -5 -3 -1 0 1 3 5 (b) -20π -10π -TC 元 10π 20π (c) -8元 -6元 -4π -2π 0 2π 4元 6元 8元 - -π/4 π/4 TC (d) 2π t Figure P.2.7-