Prove that vertical angles are congruent given a pair of intersecting lines, [math] \overleftrightarrow{AC}[/math] and [math]\overleftrightarrow{ BD}[/math].
[list=1] [*]Draw a diagram and label three adjacent angles. [*]Start with the Supplement Theorem. [*]Use substitution. [*]Use the Reflexive Property. [*]Use the Subtraction Property. [*]Use the definition of congruence. [/list]