Ray Optics

A spherical surface of radius of curvature '\(R\)' separates air from glass of refractive index 1.5. The centre of curvature is in the glass. A point object \(\mathrm{P}\) placed in air forms a real image \(\mathrm{Q}\) in the glass. The line \(P Q\) cuts the surface at point '\(O\)' and \(\mathrm{PO}=\mathrm{OQ}=\mathrm{x}\). Hence the distance '\(\mathrm{x}\)' is equal to