A periodic signal x(1) is expressed by the following Fourier series: x(t) = 3cost+ sin(r-7) - 2cos (1-7) (a) Sketch the amplitude and phase spectra for the trigonometric series. (b) By inspection of spectra in part (a), sketch. the exponential Fourier series spectra. (c) By inspection of spectra in part (b), write the exponential Fourier series for x(1). (d) Show that the series found in part (c) is equivalent to the trigonometric series for x(1).