2. $A B C D E$ - a pentagon inscribed in circle $S$. Lines $D E$ and $A B$ are parallel, $B C=C D$, $A D=D E=20, \cos C B D=5 / 8$. Find the radius of circle $S$.
Answer: 16.

## Examples of how to write answers:

## $1 / 4$

0.25

1

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