Vertical angles are pairs of non-adjacent angles formed when two straight lines intersect. They are located opposite each other at the intersection point, sharing a common vertex but not a common side. These angles appear across from each other in the "X" shape created by the intersecting lines

. A key property of vertical angles is that they are always congruent, meaning they have equal angle measures. This is known as the Vertical Angles Theorem, which states that the two opposite angles formed by the intersection of two lines are equal

. For example, if two lines intersect to form four angles labeled ∠1, ∠2, ∠3, and ∠4, then ∠1 and ∠3 are vertical angles and are equal, and similarly, ∠2 and ∠4 are vertical angles and equal

. In summary:

• Vertical angles are opposite angles formed by two intersecting lines.
• They share a common vertex but no common side.
• Vertical angles are always equal in measure (congruent).

This property holds regardless of the orientation of the lines, and vertical angles can also be right angles if the intersecting lines are perpendicular