Suppose that you have an angle modulation system with an input signal x(t) as a triangle wave of fundamental frequency 5 kHz and its most power is concentrated in the first third harmonics, the maximum and minimum voltage are 1 and -1, respectively, where one period equation of the input is x(t) = {2 * 10^4 t - 1 0 < t < T/2, -2 * 10^4 t + 3 T/2 < t < T. If carrier frequency fc = 10^6 Hz, Kf = 2000π, and Kp = π. Find the following: 1- What is the third harmonic frequency of the input signal?