Formula_7781

\[-\frac{x_{1}}{r^{3}}=-\frac{\cos \alpha}{r^{2}}, \quad-\frac{x_{2}}{r^{3}}=-\frac{\cos \beta}{r^{2}}, \quad-\frac{x_{3}}{r^{3}}=-\frac{\cos \gamma}{r^{2}},\]