equiconvex

nvex outward, the formula simplifies to: \[ \frac{1}{f} = (n - 1) \left( \frac{1}{R} - \left(- \frac{1}{R}\right) \right) = (n - 1) \left( \frac{2}{R} \right) \] This leads to: \[ \frac{1}{f} = \frac{2(n - 1)}{R} \] Rearranged to solve for n: \[ n