MathNet 2025 — 50 problems with figures (EN–VI) Question 43

Let $ABCD A'B'C'D'$ be a cube. On the segments $BC$ and $DD'$ we take the points $M$ and $N$ respectively, such that $BM = DN$. Prove that line $A'M$ is perpendicular to plane $(AB'N)$.

Cătălin Barbu