Find the radius vector defining the position of a point source of spherical waves if that source is known to be located on the straight line between the points with radius vectors \(\mathbf{r}_ {1}\) and \(\mathbf{r}_ {2}\) at which the oscillation amplitudes of particles of the medium are equal to \(a_{1}\) and \(a_{2}\). The damping of the wave is negligible, the medium is homogeneous.