

s = tf('s');

g1 = 1/((5*s + 1)*(1.8*s + 1));
g1_1 = exp(-0.9*s)/(5.9*s + 1);
g1_2 = 1/((5*s + 1)*(1.8*s + 1));

step(g1, g1_1, g1_2)
axis([-1 30 -0.02 1.02])

g3 = (-0.5*s + 1)/((5*s + 1)*(1.8*s + 1)*(0.8*s + 1));
g3_1 = exp(-2.2*s)/(5.9*s + 1);
g3_2 = exp(-0.9*s)/((5*s + 1)*(2.2*s + 1));

step(g3, g3_1, g3_2)
axis([-1 30 -0.02 1.02])