Errors associated with each respective subsystem $$\,{G_1},\,{G_2}$$ and $${G_3}$$ are $${\varepsilon _1},\,\,{\varepsilon _2}$$ and $${\varepsilon _3}$$. The error associated with the output is :

The first two rows of Routh's tabulation of a third order equation are as follows $$$\left. {\matrix{ {{s^3}} \cr {{s^2}} \cr } } \right|\matrix{ 2 & 2 \cr 4 & 4 \cr } $$$
this means there are

The unit - step response of a unity feedback system with open loop transfer function $$G\left( s \right) = {K \over {\left( {s + 1} \right)\left( {s + 2} \right)}}$$ is shown in the figure. The value of $$K$$ is

The open loop transfer function of a unity feedback system is given by $$G\left( s \right) = \left( {{e^{ - 0.1s}}} \right)/s.$$
The gain margin of this system is