why this calculations didnt show the graphics ?

%program P2_2
%Persamaan differensial
clear;
clf;
eps=-0.00000001;
syms x(t) ys(t) y(t) u(t);
x(t)=heaviside(1)*exp(-2*t);
dys=diff(ys);
y(t)=dsolve(ys+3*dys+2*diff(ys,2)==x,ys(eps)==0,dys(eps)==0);
u(t)= y(t)+5*y(t);
pretty(u(t));

[Walter Roberson]

Because the code does not contain any graphics calls?

fplot(u)

[KSSV]

There is no plot command used in your code. How you expect to get a plot?

Read about ezplot.