The function f(t) is a periodic function of period 21t. in the range (-t, 1), it equals e. if f(t) = ce denotes its fourier series expansion, the sum e.f is (1)

The function f(t) is a periodic function of period 21t. In the range (-T, 1), it equals e. If f(t) = ce denotes its Fourier series expansion, the sum e.f is (1) 1 (2) 2T sinh(27) (3) cosh(27) (4) ZT ZT