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PrintIranian Mathematical Olympiad
Iran geometry
Problem
Given two intersecting circles . Points lie on and points lie on so that are common tangents of . Let be the midpoint of . Tangent lines through to (other than ) intersect at . If be the incenter of triangle , prove that .

Solution
Suppose that touch at also let be the foot of perpendicular line through to .
Notice that . is the intersection of and incircle of triangle so Therefore hence is the midpoint of so and the result follows. ■
Notice that . is the intersection of and incircle of triangle so Therefore hence is the midpoint of so and the result follows. ■
Techniques
TangentsTriangle centers: centroid, incenter, circumcenter, orthocenter, Euler line, nine-point circleDistance chasing