t=0:0.01:6;
f=cos(t);
c=cos(100*t);
f1=(1+f).*c;
f2=(1+0.707*cos(t-pi/4)).*c;
subplot(2,1,1)
plot(t,f1);grid on;ylabel('the input signal s(t)')
subplot(2,1,2)
plot(t,f2);grid on;xlabel('time t');ylabel('the output signal v2(t)')