Answer:
Two angles are vertical angles if and only if they are congruent.
Explanation:
A biconditional statement is a statement that combines a conditional statement and its converse, using the phrase "if and only if." In this case, the original statement is "If two angles are vertical angles, then they are congruent." To convert this into a biconditional statement, we need to include the converse as well. The converse of the original statement is "If two angles are congruent, then they are vertical angles."
Combining the original statement and its converse, we get the biconditional statement:
Two angles are vertical angles if and only if they are congruent.