Problem $(2)$: Consider a rectangular block with cross section $2L21.$ All its surfaces are maintained at temperature $T_0$ and there is a volumetric heat generation of $Q^{}$ within the block. Show that steady state $2-$D temperature distribution $T(x,y)$ is given by

$\frac{T(x,y)-T_0}{(\frac{Q{L}^2}{k})}=\frac{1}{2}[1-(\frac{x}{L}{)}^2]-2{\displaystyle \underset{n=0}{\overset{}{}}}\frac{(-1{)}^n}{({}_{n}L{)}^3}(\frac{cosh({}_{n}y)}{cosh({}_{n}l)})cos({}_{n}x)$

where ${}_{n}L=(2n+1)\frac{}{2},n=0,1,2,$dotsdots