The considered electrical circuit is analyzed as an object which is to be controlled automatically, therefore, its transmittance and state space representation equations will be written down.

Transmittance is given by formula

H(s) = \frac{Y(s)}{U(s)}State space representation equations

\dot{ \textbf{x} } = A \cdot \textbf{x} + B \cdot \textbf{u} \textbf{y} = C \cdot \textbf{x} + D \cdot \textbf{u}An example which is solved step by step for the considered electric circuit can be found here