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PrintSAUDI ARABIAN MATHEMATICAL COMPETITIONS
Saudi Arabia geometry
Problem
Let be a triangle inscribed in the circle and is a point inside the triangle . Let be a point on such that . The line cuts the perpendicular bisector of at . The line cuts the line passing through and is perpendicular to at . Let be the reflection of through . Prove that .

Solution
Let be the midpoints of . Since is cyclic Hence the isosceles triangles and are similar. The line cuts at . We have Easily seen and . Hence, . We deduce . This, triangle is right at . We are done.
Techniques
Cyclic quadrilateralsAngle chasingDistance chasingConstructions and loci