Its wished to prepare four lenses double convex, convexo concave double concave and concavo- convex by the two cusued surfaces of radii of curvature +20cm and +30cm of refractive index 1.5. What are the values of their focal lengths in the given order.

Its wished to prepare four lenses double convex, convexo concave doubl

1.	Its wished to prepare four lenses double convex, convexo concave double concave and concavo- convex by the two cusued surfaces of radii of curvature +20cm and +30cm of refractive index 1.5. What are the values of their focal lengths in the given order.
Answer» `+20CM,-20cm,+120CM,-120cm` `+120cm,-120cm,-20cm,+20cm` `-120cm,+120cm,-20cm,+120cm` `-20cm,-120cm,-20cm,+120cm` ANSWER :D