2.1求解第二个方程 \frac{1}{g}\frac{\partial^2 g(\varphi)}{\partial \varphi^2}=-v^2 \\\frac{d^2 g(\varphi)}{d \varphi^2}+v^2g(\varphi)=0 \\特征方程为:r^2+v^2=0 \Rightarrow r=±j|v| \\g(\varphi)=A'e^{r_1 \varphi}+B'e^{r_2 \varphi}=A'e^{jv\varphi}+...