Problem $(2)$: Consider an infinitely long two$-$dimensional fin of thickness $l.$ The base temperature of the fin is $T_b$ and the ambient temperature is $T_{}.$ The heat transfer coefficient $h$ is large. Show that the temperature distribution $T(x,y)$ is given by:

$\frac{T(x,y)-T_{}}{T_b-T_{}}=\frac{2}{}{\displaystyle \underset{n=1}{\overset{}{}}}\frac{[1-(-1{)}^n]}{n}$exp$(-\frac{nx}{l})sin(\frac{ny}{l})$