Find the largest incident angle at the interface between the cover glass and the sample for an air objective with numerical aperture n a = 0.9, if the refractive index of the cover glass is n g =...

Find the largest incident angle at the interface between the cover glass and the sample for an air objective with numerical aperture n_a
= 0.9, if the refractive index of the cover glass is n_g
= 1.52. How is this angle changed if the air objective has a numerical aperture of n_a
= 0.4? How is this angle changed if the air objective is replaced by an oil objective with numerical aperture n_a
= 1.45?