VTMO 2026 - Grade 8 - Semifinal - SET 1 - Self-study Question 18

Quadrilateral $ABCD$ has $\angle BCD=90^\circ$, $\angle ABC=150^\circ$ and $CD=AB$. Points $M,N$ are the midpoints of $BC,AD$, respectively. Find the acute angle between $MN$ and $BC$.