Consider the cosine and the sine transforms: de ( wj ) = 1/ 2 Et=1 Xt Cos(2Twit), ds (wj) = 1/z Zt=1 Xt sin(2nwit), j= 0, ..., n- 1 Then show that n n couldc (w;), dc.(wk)] = 7 ( t - s) cos ( 2 TW; s ) cos ( 2 TWkt), s=1 t=1 (5) n n doesn't couldc (wj), ds( wk) ] = 7 ( t - s ) cos ( 2 TW; s ) sin ( 2 TTWKt)