View source for Vertical Angle Theorem

The '''Vertical Angle Theorem''' is a [[theorem]] that states that all [[vertical angles]] are congruent.
==Proof==
Assume all angle measures to be in [[radians]]. A pair of vertical angles are formed by [[line|lines]] <math>\overline A \overline B</math> and <math>\overline C \overline D</math> and the intersection of these lines is P. Angles <math>\angle APC</math> and <math>\angle BPD</math> are vertical angles. Let <math>m \angle APC = x</math>. From this, <math>m\angle CPB = \pi-x</math>, so <math>m \angle BPD = \pi-(\pi-x)=x=m\angle APC.</math>
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