The focal length of a lens of power + 4D is

power 4d6. A convex lens of power +6 D is placed in contact with a concave lens of power –4D. What will be the nature and focal length of this combination ? (a) convex, 100 cm (b) convex, 50 cmWe show a universal 4D printing technology for manufacturing MXene hydrogels with customizable geometries, which suits a family of MXenes.