Vertically Opposite Angles Two angles are called a pair of vertically opposite angles, if their arms form two pairs of opposite rays. Let two lines AB and CD intersect at a point O. Then, two pairs of vertically opposite angles are formed. (i) ∠AOC and ∠BOD (ii) ∠AOD and ∠BOCTheorem 1: If two lines intersect then the vertically opposite angles are … [Read more...] about Vertically Opposite Angles