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jmc

geometry senior

Problem

Let have side lengths , , and . Point lies in the interior of , and points and are the incenters of and , respectively. Find the minimum possible area of as varies along .
Solution
First note thatis a constant not depending on , so by it suffices to minimize . Let , , , and . Remark thatApplying the Law of Sines to givesAnalogously one can derive , and sowith equality when , that is, when is the foot of the perpendicular from to . In this case the desired area is . To make this feasible to compute, note thatApplying similar logic to and and simplifying yields a final answer of
Final answer
126