Four particles each of mass \( M \), move along a circle of radius \( R \) under the action of their mutual gravitational attraction as shown in figure. The speed of each particle is:
\( \dfrac{1}{2} \sqrt{ \dfrac{GM}{R} \, (2\sqrt{2} - 1) } \)
\( \dfrac{1}{2} \sqrt{ \dfrac{GM}{R} \, (2\sqrt{2} + 1) } \)
\( \dfrac{1}{2} \sqrt{ \dfrac{GM}{R \, (2\sqrt{2} + 1)} } \)
\( \sqrt{\dfrac{GM}{R}} \)