$ \frac{d^{2} y(t)}{d t^{2}}-\frac{d y(t)}{d t}-2 y(t)=x(t) $ ;

i) Determine H(s) as a ratio of two polynomials in s. Sketch the pole zero pattern of H(s).

ii) Determine h(t) for each of the following cases :

1. The system is stable.

2. The system is casual.

3. The system is neither stable now casual.