Modify tf_demo.m to do the following:

---tf demo--

num = [1]; den=[1 4 20];

sys=tf(num,den); % 1/(s^2 + 4s + 20)

step(sys) %very powerful and easy to use pause

impulse(sys) % also powerful and easy to use pause

t = 0:0.1:20; % vector of time samples u = 3*sin(t); % the INPUT valuse

lsim(sys,u,t) %plot the response and the input pause

y=lsim(sys,u,t); plot(t,y);

a) Use the tf() function to define a system variable for: 8 +48 +63 +8x = f(t) Use the step() function to plot the response of the system for f(t)= u(t) (a unit step). a) Use the tf() function to define a system variable for: 8 +48 +63 +8x = f(t) Use the step() function to plot the response of the system for f(t)= u(t) (a unit step)