2 answers
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AM¯¯¯¯¯¯¯¯¯ ≅ BM¯¯¯¯¯¯¯¯¯
AB¯¯¯¯¯¯¯¯ is the diameter of the large circle.
CD¯¯¯¯¯¯¯¯ is the diameter of the small circle.