MathDB
right angle wanted, starting with a trapezoid with perpendicular diagonals

Source: 2018 Oral Moscow Geometry Olympiad grades 10-11 p2

July 25, 2019
geometrytrapezoidperpendiculardiagonalsright angle

Problem Statement

The diagonals of the trapezoid ABCDABCD are perpendicular (AD//BC,AD>BCAD//BC, AD>BC) . Point MM is the midpoint of the side of ABAB, the point NN is symmetric of the center of the circumscribed circle of the triangle ABDABD wrt ADAD. Prove that ∠CMN=90o\angle CMN = 90^o.
(A. Mudgal, India)
Back to ProblemsView on AoPS