$3\mathrm{.}35.$ Consider a continuous$-$time LTI system S whose frequency response is H$($jw$)=\{$ I, $0,$ lwl $2$: $250$ otherwise $$ When the input to this system is a signal x$($t$)$ with fundamental period T $=7$r$/7$ and Fourier series coefficients ah it is found that the output y$($t$)$ is identical to x$($t$).$ For what values of k is it guaranteed that ak $=$ O$?$