% file: task20.m
% Filter with the frequency response:
%  H(e^jw) = 1 + 0.1 e^-jw + 0.9 e^-j2w
B = [1  0.1  0.9];
A = [1];
figure(1); clf;  % open/activate Figure No 1 + clean
freqz(B, A);     % ampl.response + phase response 
figure(2); clf;
impz(B, A);      % impulse response h[n]
