An object is placed beyond the centre of curvature $C$ of the given concave mirror. If the distance of the object is $d_{1}$ from $C$ and the distance of the image formed is $d_{2}$ from $C$, the radius of curvature of this mirror is:\\
(1) $\frac{2d_{1}d_{2}}{d_{1}+d_{2}}$\\
(2) $\frac{2d_{1}d_{2}}{d_{1}-d_{2}}$\\
(3) $\frac{d_{1}d_{2}}{d_{1}+d_{2}}$\\
(4) $\frac{d_{1}d_{2}}{d_{1}-d_{2}}$