Problem 24 (2025 AMC 12A)
AMC 12AHard
From module Law of Cosines
Problem
A circle of radius r is surrounded by n circles of radius R externally tangent to the central circle and sequentially tangent to each other. Then r/R can be written as (a - b√c)/d where a, b, c, d are integers. What is a + b + c + d?