h=.01;
t=0:h:20;
y1=zeros(1,length(t));
y2=zeros(1,length(t));
y3=zeros(1,length(t));
y4=zeros(1,length(t));
y1(1)=0.2;
y2(1)=1;
y3(1)=0;
y4(1)=0;
N=length(t);
for i=1:N-1
y1(i+1)=y1(i)+h*y2(i);
y2(i+1)=y2(i)+h*(cos(3*t(i))-4*y2(i)+y4(i)-5*y1(i)+3*y3(i));
y3(i+1)=y3(i)+h*y4(i)...