Prove vertical angles are congruent.
I don't yet know degrees. All I know is congruent angles have congruent supplements. Is it too easy to just say that if I have two intersecting lines AC and BD and their intersecting point is X. < CXD is supplementary to < CXB by theorem. And < CXB is supplementary to < BXA. Thus < CXD must be congruent to < BXA because they share the same supplement? I feel like I am missing something.
Yes, that's all there is to it.