High Quality Content by WIKIPEDIA articles! In geometry, a pair of angles is said to be vertical (also opposite and vertically opposite) if the angles are formed from two intersecting lines and the angles are not adjacent. They all share a vertex. Such angles are congruent and thus are equal in measure.When two straight lines intersect at a point, four angles are formed.The nonadjacent angles are called vertical or opposite angles. Also, each pair of adjacent angles form a straight line and are supplementary. Since any pair of vertical angles are supplementary to either of the adjacent angles, the vertical angles are congruent.