## Geometry: Common Core (15th Edition)

$\overline{AB}$ is parallel to $\overline{CD}$.
We could call $\angle ABC$ and $\angle DCB$ alternate interior angles. If two lines or line segments are cut by a transversal, and alternate interior angles are equal, then those lines or line segments are parallel. We see from the diagram that $\angle ABC$ and $\angle DCB$ are congruent; therefore, $\overline{AB}$ is parallel to $\overline{CD}$.