Geometry: Need help with vertical angles.?

Question

There is something wrong with this definition for a pair of vertical angles: "If LINE AB and LINE CD intersect at point P, then ANGLE APC and ANGLE BPD are a pair of vertical angles are a pair of vertical angles. Stetch a counterexample to show why it is not correct. Can you add a phrase to correct it.

Answer 1

Counterexample:

If C and D are both on the same side of AB, then angles APC and BPD are not a pair of vertical angles.

Correction:

If line segment AB and line segment CD intersect at point P, then angle APC and angle BPD are a pair of vertical angles.