MathNet 2022-part-01 — 197 problems (EN–VI) Question 14

Let $ABCD$ be a parallelogram whose diagonals meet at $M$. Let $N$ be an interior point of triangle $AMB$ such that $\angle AND = \angle BNC$. Prove that $\angle MNC = \angle NDA$ and $\angle MND = \angle NCB$.