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1997 USAMO Problems/Problem 2

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Problem

\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.

Solution

This problem needs a solution. If you have a solution for it, please help us out by adding it.

Let the perpendicular from A meet FE at A'. Define B' and C' similiarly. By Carnot's Thereom, The three lines are concurrent if

FA'^2-EA'^2+EC'^2-DC'^2+DB'^2-FB'^2 = AF^2-AE^2+CE^2-CD^2+BD^2-BF^2 = 0

But this is clearly true, since D lies on the perpendicular bisector of BC, BD = DC.

QED

1997 USAMO (Problems)
Preceded by
Problem 1
1 2 3 4 5 Followed by
Problem 3
All USAMO Problems and Solutions
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