Choose one of the following theorems and prove it: Vertical Angles are congruent, Alternate interior angles are congruent, Corresponding angles are congruent. Demonstrate on a whiteboard.

(Just tell me how to write it on a whiteboard)

As can be seen from the figure above, when two lines intersect, four angles are formed. Each opposite pair are called vertical angles and are always congruent. The red angles ∠JQM and ∠LQK are equal, as are the blue angles ∠JQL and ∠MQK. Vertical angles are also called opposite angles.