Linear PDEs

Use the mean value formulas to prove that (for $n\geq 3$) u(0) = \frac{1}{n \alpha(n)r^{n-1}}\int_{\partial B\left(0,r\right)} g \, dS + \frac{1}{n\left(n-2\right) \alpha \left(n\right)} \int_{B\left(...