If two angles are vertical angles, then they are congruent. Vertical angles are defined as the angles opposite each other when two lines intersect. According to the vertical angles theorem, vertical angles are always equal in measure, meaning they have the same degree of measurement. This is a fundamental property in geometry and is often used in proofs and problem- solving tasks. When two lines intersect, they form four angles, and the pairs of vertical angles are the opposite angles that do not share a common side but share a common vertex. These opposite angles are always congruent (equal in measure) due to the vertical angles theorem, which can be proven using the properties of linear pairs of angles and the transitive property of equality. In summary, the statement "if two angles are vertical angles, then they are congruent" is true and is a key principle in geometry about intersecting lines and angles.