\[\phi=\sin ^{-1}\left(\frac{x_{1}}{x_{2}}\right)=\sin ^{-1}\left(\frac{y_{1}}{y_{2}}\right)\]
\[\text{Second possibility} =360^{\circ}-\phi\]
\[\phi=180^{\circ}-\sin ^{-1}\left(\frac{x_{1}}{x_{2}}\right)\]
\[\text{Second possibility} =360^{\circ}-\phi\]