$\therefore$ the polytropic exponent $\eta=-2$
Work done in a polytropic process is
$W=\frac{-n R \Delta T}{\eta-1}$ $...(1)$
Substituting $\Delta T=T_{2}-T_{1}$ and $\eta=-2$ in $( 1)$
$W=\frac{-R\left(T_{2}-T_{1}\right)}{-2-1}=\frac{1}{3} R\left(T_{2}-T_{1}\right)$

