An object is located 36 cm to the left of a biconvex lens of index of regraction 1.5. The left surface of the lens has a radius of curvature of 20 cm. The right surface of the lens is to be shaped so that a real image will be formed 72 cm to the right of the lens. What is the required radius of curvature for the second surface? I asked earlier on this, but I still got it wrong: this is what I did - I used 1/F=(n-1)(1/R1 + 1/R2) 1/72 = (1.5 - 1) (1/.2 + 1/R2) Solved it and got R2 to equal 45 cm. I am pretty sure 1/F shouldnt be 72, but if its unknown that would make it unsolvable unless I am missing something?