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 ∠BOC
Theorem 1:
If two lines intersect then the vertically opposite angles are equal.
