[ Properties and characteristics of a parallelogram ] Law of Cosines $\quad]$

The sides of a parallelogram are 2 and 4, and the angle between them is $60^{\circ}$. Through the vertex of this angle, lines are drawn passing through the midpoints of the other two sides of the parallelogram. Find the cosine of the angle between these lines.
Let $M$ and $N$ be the midpoints of sides $B C$ and $C D$ of parallelogram $A B C D$. Find the sides of triangle $A M N$.

## Answer

$\frac{5}{2 \sqrt{7}}$.