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Carnot's Thereom

From AoPSWiki

Carnot's Theorem states that in a triangle ABC with A_1\in BC, B_1\in AC, and C_1\in AB, perpendiculars to the sides BC, AC, and AB at A_1, B_1, and C_1 are concurrent if and only if A_1B^2+C_1A^2+B_1C^2=A_1C^2+C_1B^2+B_1A^2.

Contents

Proof

This proof is incomplete. You can help us out by completing it.

Problems

Olympiad

\triangle ABC is a triangle. Take points D, E, F on the perpendicular bisectors of BC, CA, AB respectively. Show that the lines through A, B, C perpendicular to EF, FD, DE respectively are concurrent. (Source)

See also

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