Prove that vertical angles are congruent given a pair of intersecting lines, [math]\overleftrightarrow{AC}[/math] and [math]\overleftrightarrow{BD}[/math].

[list=1][br][*]Draw a diagram and label three adjacent angles.[br][*]Start with the Supplement Theorem.[br][*]Use substitution.[br][*]Use the Reflexive Property.[br][*]Use the Subtraction Property.[br][*]Use the definition of congruence.[br][/list][br][br]This applet is provided by Walch Education as supplemental material for their mathematics programs. Visit www.walch.com for more information.[br]