Posted by Max on .
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.
What is wrong??!?

Geometry 
Martin,
Well, the only thing I can see "lacking" in the definition is if the intersection P is actually also one of the A,B,C,D points. So you could just say ""If line AB and line CD intersect at point P such that P is different from A, B, C or D, then angle APC and angle BPD are a pair of vertical angles."