Explain Angle Theorems ?

Certain angles and angle pairs have special characteristics: Vertical angles are opposite angles formed by the intersection of two lines. Vertical angles are congruent (that is, they have the same measure).

Two lines are perpendicular if they form a right angle.

If two parallel lines are cut by a transversal, then alternate interior angles are congruent. The picture below shows two pairs of alternate interior angles: angles C and D; angles E and F.

If two parallel lines are cut by a transversal, then corresponding angles are congruent. The picture below shows two pairs of corresponding angles: angles G and H; angles I and K.