GKFix MCQ Question

In the derivation, what is the specific condition applied to Eq. (9.19) to obtain Eq. (9.20)?

• A. The object distance OB is considered to approach infinity (OB → ∞), and DI is set equal to the focal length f
• B. The lens thickness is set to zero
• C. The refractive index n2 is set equal to n1
• D. The radii of curvature R1 and R2 are made equal