$\begin{aligned} & \text { [ Congruent triangles. Criteria for congruence ] } \\ & \text { [Central symmetry helps solve the problem].] }\end{aligned}$

Segments $A B$ and $C D$ intersect at point $O$, which is the midpoint of each of them. What is the length of segment $B D$ if segment $A C=10$?
Triangle $B O D$ is equal to triangle $A O C$ by two sides and the included angle. Therefore, $B D=A C=10$.



## Answer

10.