Ответ:
\[B\left( \frac{1}{2};\frac{\sqrt{3}}{2} \right);\ \ C\left( - \frac{1}{2};\ - \frac{\sqrt{3}}{2} \right);\ \ \]
\[\alpha = 60{^\circ};\ \ \beta = 240{^\circ}.\]
\[B\left( \frac{1}{2};\frac{\sqrt{3}}{2} \right);\ \ C\left( - \frac{1}{2};\ - \frac{\sqrt{3}}{2} \right);\ \ \]
\[\alpha = 60{^\circ};\ \ \beta = 240{^\circ}.\]