作者Zyca (swun mitru valy)
标题[转录]◇ IMO 竞赛第一题
时间Wed Jan 5 20:24:57 2000
In the convex quadrilateral（凸四边形） ABCD, the diagonals AC and BD
are perpendicular and the opposite sides AB and DC are not parallel.
Suppose that the point P,where the perpendicular bisectors（中垂线）
of AB and DC meet, is inside ABCD.Prove that ABCD is a cyclic
quadrilateral（圆内接四边形） if and only if the triangles ABP and CDP
have equal areas.
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