Step Response of Transfer Function

Hello so am trying to plot the step response of this trasnsfer function , but am not really sure how do i need to write it down in den = part , any help would be great thanks. .

t=0:0.01:5;

num = 1;

den = [1 2 17];

sys = tf(num, den);

y = step(sys,t);

plot(t,y*4)

[Sam Chak]

The original question may be beneficial to people who wish to learn how to plot the step response.

[Rena Berman]

(Answers Dev) Restored edit

Answer 1

[Yongjian Feng]

Get help by doing:

help tf

Basically, you need to expand the denominator given in image into polynomial of s. Then take the coefficients and put into den. For example, if you expand it into 2*s^2+5*s+10, then den = [2 5 10].

To expand the denominator, you can do it manually or you can use the expand function of matlab.