MathDB

1

Part of 2005 China Second Round Olympiad

Problems(1)

Lines pass through incenter and excenter

Source: 2005 China Second Round Olympiad

9/2/2014
In △ABC\triangle ABC, AB>ACAB>AC, ll is a tangent line of the circumscribed circle of △ABC\triangle ABC, passing through AA. The circle, centered at AA with radius ACAC, intersects ABAB at DD, and line ll at E,FE, F. Prove that lines DE,DFDE, DF pass through the incenter and an excenter of △ABC\triangle ABC respectively.
geometryincentercircumcircle