^Curved surface refraction formula

It is a general expression, applicable to both convex & concave surface, for both point & extended object placed in any medium rare or denser, for any type of image formed (real or virtual).

While using this result keep in mind following points:

1. All distance are measured from the pole P (i.e. the centre of surface at which incident ray strikes.
2. μ₁ → Medium from which incident ray comes.
3. μ₂ → Medium towards which incident ray is sent.