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 t = 0:0.1:20; u = 3*sin(t); % vector of time samples % the INPUT valuse %plot the response and the lsim(sys,u,t) input pause y=lsim(sys,u,t); plot(t,y); 3. Modify tf_demo.m to do the following: a) Use the tf() function to define a system variable for: 8+48 +68+8x = f(t) Use the step() function to plot the response of the system for f(t)= u(t) (a unit step)