The document discusses triangular wave functions and half-wave rectified sinusoidal functions. It defines a triangular wave function with period 2a and amplitude Xo that is shifted down by -Xo/2. It also defines a half-wave rectified sinusoidal function as the positive part of a sinusoid with period π, equal to sin(t) from 0 to π and 0 from π to 2π. The Fourier series representations of these functions are presented.