** INSERT APP THAT SHOWS VERTICAL ANGLES **
 Manipulative 1: Vertical angles. 

Vertical angles are a pair of
angles
formed by
intersecting
lines that are opposite each
other. Each pair of intersecting lines forms four angles and two pair of vertical angles.
Vertical Angle Congruence Theorem
The Vertical Angle Congruence Theorem shows that vertical angles are always congruent.
Step  Description  Justification 
1  Angles 1 and 2 are supplementary.  The definition of supplementary angles. 
2  Angles 2 and 3 are supplementary.  The definition of supplementary angles. 
3  Angles 1 and 3 are congruent. Q.E.D.  The Supplementary Angle Congruence Theorem 
Table 1: Proof of the Vertical Angle Congruence Theorem 
