Alternate Angles: Definition and Types

In this tutorial we will learn definition and types of alternate angles.

In geometry, alternate angles are a special kind of angles.

Alternate interior angles are formed when a transversal intersect two parallel or non-parallel lines.

If a straight line intersects two lines, in the same plane at two distinct points, then it is called a transversal.

If two parallel lines are intersected by transversal line, then the pairs of alternate angles are congruent.

If the alternate angles are equal, then two lines are parallel.

When two parallel or non-parallel lines are intersected by a transversal, they form eight (8) angles.

∠1 , ∠2, ∠8 and ∠7 are located on the outer side of two lines.

∠4 , ∠3, ∠5 and ∠6 are located on the inner side of two lines.

Type of alternate angles.

There are two types of alternate angles depend on the position of angles.

1. Alternate interior alternate angles and
2. Alternate exterior angles

Alternate interior angles

Alternate angles are the pair of angles on the inner or interior side of the two parallel lines but on the opposite side of the transversal.

These angles are set of non-adjacent angles on either side of the transversal.

Alternate exterior angles

Alternate exterior angles are the pair of angles on the outer or exterior side of the two parallel lines but on the opposite side of the transversal line.

When a transversal intersects two or more parallel lines, the alternate angles are always equal. These pairs of alternate angles and are always equal.

Remember: Alternate angles are the angles, formed when two parallel or non-parallel lines are intersected by a transversal.