%  Figure 6.2
%
Omega = -pi:2*pi/300:pi;
a = 0.5;
X = 1./(1-a*exp(-j*Omega));
subplot(211),plot(Omega/pi,abs(X));
ylabel('|X(  )|')
subplot(212),plot(Omega/pi,180*angle(X)/pi);
ylabel('  X(  )');
