@Abhijit_Chowdhary, sorry but I’ve deleted my previous post as the answer was not general. Meanwhile, I am linking this other post where the Fourier coefficients were written more carefully by following their definition.
@Abhijit_Chowdhary, sorry but I’ve deleted my previous post as the answer was not general. Meanwhile, I am linking this other post where the Fourier coefficients were written more carefully by following their definition.