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AMO-Bench 2025 Problem 37

  • Answer

In △ABC\triangle ABC with AB<AC<BCAB < AC < BC, let OO and II be its circumcenter and incenter, respectively. Let MbM_b and McM_c be the midpoints of the arc ACAC (not containing BB) and the arc ABAB (not containing CC), respectively, on the circumcircle ⊙O\odot O. Let SbS_b be a point on ⊙O\odot O such that ISb⊥BSbIS_b \perp BS_b, and let ScS_c be a point on ⊙O\odot O such that ISc⊥CScIS_c \perp CS_c. Let HaH_a be the intersection of lines MbScM_bS_c and McSbM_cS_b. Points HbH_b and HcH_c are defined analogously.It is given that the lines AHa,BHb,CHcAH_a, BH_b, CH_c are pairwise non-parallel. Let GG be the centroid of the triangle formed by these lines (if the three lines are concurrent, GG is defined as their point of concurrency). Let the side lengths of △ABC\triangle ABC be BC=aBC = a, CA=bCA = b, and AB=cAB = c. Find the product of the distances from point GG to the lines IHa,IHb,IHcIH_a, IH_b, IH_c. (Expressed in terms of a,b,ca, b, c and simplified completely.)

Dataset text AMO-Bench. Open licence.

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\frac{(a-b)(a-c)(b-c)}{8}\cdot \left( \frac{(a+b-c)(a-b+c)(-a+b+c)}{2abc-(a+b-c)(a-b+c)(-a+b+c)} \right)^3

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