MathDB

1

Part of 2011 Danube Mathematical Competition

Problems(1)

equal angles with an interior point of a parallelogram, easy danube geometry

Source: Danube 2011 P1

9/8/2018
Let ABCMABCM be a quadrilateral and DD be an interior point such that ABCDABCD is a parallelogram. It is known that ∠AMB=∠CMD\angle AMB =\angle CMD. Prove that ∠MAD=∠MCD\angle MAD =\angle MCD.
geometryparallelogramequal anglesquadrilateral