Question

Definition, Property, Postulate, or Theorem that justifies
If angle 1 and angle 2 are vertical angles, then angle 1 is congruent to angle 2.

Answer 1

It's a theorem since it can be proved.

Answer 2

but what is the theorem? @mathstudent55

Answer 3

"If two angles are vertical, then they are congruent."
More simply, "Vertical angles are congruent"

Answer 4

There is the proof. now you know for sure this is a theorem.

Answer 5

thank you so much! @mathstudent55

Answer 6

You're welcome.