Question 5
The trapezoid $ABCD$ is inscribed in the circle $\mathcal{K}$. The lines containing the sides $AD$ and $BC$ intersect at the point $M$, and the tangents to the circle $\mathcal{K}$ at the points $B$ and $D$ intersect at the point $N$. Prove that the segments $MN$ and $AB$ are parallel.