想保留的成分为cos(2*π*n/3) 带通滤波器，滤除1+cos(2*π*n/3) 的成分，即想保留的成分为cos(π*n/4) 带阻滤波器，滤除cos(π*n/4) 的成分，-Want to keep the ingredients for the cos (2* π* n/3) band-pass filter, filter 1+ Cos (2* π* n/3) of the composition, that is, want to keep the ingredients of cos (π* n/4 ) band-stop filter, filter cos (π* n/4) of the composition,