Marinada '15

%V0 Neka je $f : \mathbb{Z} \to \mathbb{Q}$ takva da vrijedi $f \left( 1 \right)=2$ i $$ f \left( n+1 \right)= \frac{1+f \left( n \right)}{1-f \left( n \right)}, \, \, \, \text{za svaki } n \in \mathbb{Z}.$$ Odredite $f\left(-73\right)$.