2. The following functions are assumed to be 27-periodic. Find the Fourier series expansion for each function and then plot graphs of the first three partial sums. (a) f(t) = t for 0 < t < 2. (b) f(t) = t +t for < t < . - (c) f(t) = 1- for 0 t 2 T (d) f(t) = t for - < t