Example 7. If [tex]\theta = t^n e^{\frac{-r^2}{4 t}}[/tex], find the value of [tex]n[/tex] which will make [tex]\frac{1}{r^2} \frac{\partial}{\partial r}\left(r^2 \frac{\partial \theta}{\partial r}\right) = \frac{\partial \theta}{\partial t}[/tex].