Interior angles the angles whose arms include line segment PQ are called interior angles.

exterior angles the angles whose arms do not include the line segment PQ are called exterior angles.

EXTERIOR ANGLES The angles whose arms do not include the line segment PQ are called exterior angles.

Interior opposite angles

Interior adjacent angles

Interior of an angle

ALTERNATE EXTERIOR ANGLES A pair of angles in which one arm of each of the angles is on opposite sides of the transversal and whose other arms are directed in opposite direction and do not include segment PQ is called a pair of alternate exterior angles.

Alternate exterior angles a pair of angles in which one arm of each of the angles is on opposite side of the transversal and whose other arms are directed in opposite direction and do not include segment PQ is called a alternate exterior angles.

When given two lines are parallel. If one angle of two interior angle is 70^(@) then find the measure of second interior angle.

Alternate interior angles a pair of angles in which one arm of each of the angle is on opposite sides of the transversal and whose other arms include segment PQ as shown in Fig.15.15 is called a pair of alternate interior angles.

In the adjoining figure,identify ( i ) the pairs of corresponding angles.(ii) the pairs of alternate interior angles.(iii) the pairs of interior angles on the same side of the transversal.(iv) the vertically opposite angles.