Rectangular sheet of paper $ABCD$ is folded as shown in the figure. Find the rato $DK: AB$, given that $C_1$ is the midpoint of $AD$.
Problem
Source: V.A. Yasinsky Geometry Olympiad 2017 VIII-IX p1 [Ukrane]
Tags: geometry, rectangle, ratio
Source: V.A. Yasinsky Geometry Olympiad 2017 VIII-IX p1 [Ukrane]
Tags: geometry, rectangle, ratio
Rectangular sheet of paper $ABCD$ is folded as shown in the figure. Find the rato $DK: AB$, given that $C_1$ is the midpoint of $AD$.