Ответ:
\[B\left( \frac{1}{2};\frac{\sqrt{3}}{2} \right);\ \ C\left( - \frac{1}{2};\frac{\sqrt{3}}{2} \right);\ \ \]
\[\alpha = \frac{\pi}{3};\ \ \beta = \frac{2\pi}{3}.\]
\[B\left( \frac{1}{2};\frac{\sqrt{3}}{2} \right);\ \ C\left( - \frac{1}{2};\frac{\sqrt{3}}{2} \right);\ \ \]
\[\alpha = \frac{\pi}{3};\ \ \beta = \frac{2\pi}{3}.\]