Which assumption(s) must be used to prove that vertical angles are congruent?

The assumption to prove that vertical angles are congruent is "Vertical angles are always congruent".

Step-by-step explanation:

Vertical angles are a pair of angles (not adjacent) opposite each other by a vertex when two lines intersect.

When two lines intercept at a point, 4 angles are formed. Those that are opposite to each other and are not adjacent are vertical angles, these are always congruent.

In this case, we can affirm that if two angles are opposed by the vertex, they are equal.

Have a nice day!

answer: the answer to your question is parallel