(Solved): 3. "Know thy enemy" is a saying in English which, when applied to control theory, means that for s ...

3. "Know thy enemy" is a saying in English which, when applied to control theory, means that for succesful control of a given system, the controler must contain a copy of the given system. One popular such form is this closed loop system: The gray box is the controller, and it contains a copy of the given system $$P$$. Notice that here $$\hat{r}=e+z$$. (a) Show that $$H_{y/r}(s)=P(s)Q(s)$$.