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Let-M-be-a-point-in-the-interior-of-the-equilateral-triangle-ABC-and-let-A-B-and-C-be-its-projections-onto-the-sides-BC-CA-and-AB-respectively-Prove-that-the-sum-of-lengths-of-the-inradii-of-tr




Question Number 16739 by Tinkutara last updated on 26/Jun/17
Let M be a point in the interior of the  equilateral triangle ABC and let A′,  B′ and C′ be its projections onto the  sides BC, CA and AB, respectively.  Prove that the sum of lengths of the  inradii of triangles MAC′, MBA′ and  MCB′ equals the sum of lengths of the  inradii of trianges MAB′, MBC′ and  MCA′.
$$\mathrm{Let}\:{M}\:\mathrm{be}\:\mathrm{a}\:\mathrm{point}\:\mathrm{in}\:\mathrm{the}\:\mathrm{interior}\:\mathrm{of}\:\mathrm{the} \\ $$$$\mathrm{equilateral}\:\mathrm{triangle}\:{ABC}\:\mathrm{and}\:\mathrm{let}\:{A}', \\ $$$${B}'\:\mathrm{and}\:{C}'\:\mathrm{be}\:\mathrm{its}\:\mathrm{projections}\:\mathrm{onto}\:\mathrm{the} \\ $$$$\mathrm{sides}\:{BC},\:{CA}\:\mathrm{and}\:{AB},\:\mathrm{respectively}. \\ $$$$\mathrm{Prove}\:\mathrm{that}\:\mathrm{the}\:\mathrm{sum}\:\mathrm{of}\:\mathrm{lengths}\:\mathrm{of}\:\mathrm{the} \\ $$$$\mathrm{inradii}\:\mathrm{of}\:\mathrm{triangles}\:{MAC}',\:{MBA}'\:\mathrm{and} \\ $$$${MCB}'\:\mathrm{equals}\:\mathrm{the}\:\mathrm{sum}\:\mathrm{of}\:\mathrm{lengths}\:\mathrm{of}\:\mathrm{the} \\ $$$$\mathrm{inradii}\:\mathrm{of}\:\mathrm{trianges}\:{MAB}',\:{MBC}'\:\mathrm{and} \\ $$$${MCA}'. \\ $$

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