clear x
a=pi/4;
n=0:1:50;
x(n+1)=5*cos(a*a*n);
figure(1)
stem(n,x,'linewidth',2)
xlabel('n');
ylabel('x(n)');

clear x
a=5;
c=abs(0.5+0.5*j);
n=0:1:50;
for m=0:50
    x(m+1)=a*c^m;
end
figure(2)
stem(n,x,'linewidth',2)
xlabel('n');
ylabel('x(n)');