What are Alternate Interior Angles?

Alternate interior angles are pairs of angles that lie on opposite sides of a transversal line and inside a pair of lines but on opposite sides of the transversal. These angles are formed when a transversal intersects two parallel lines.

The key property of alternate interior angles is that they are equal in measure. In other words, if two parallel lines are intersected by a transversal, then the pairs of alternate interior angles are congruent.

Alternate Interior Angles Definition

The angles created on opposing sides of the transversal are known as alternate internal angles.

In other words, when two parallel lines are crossed by a transversal, eight angles are generated. The alternate interior angles are those that are on the inner side of the parallel lines but on the opposite sides of the transversal.

Alternate Interior Angles Examples

Let’s consider a pair of parallel line and a transversal as shown in the figure below:

The inner angles are angles ∠3, ∠4, ∠5, and ∠6. Out of these ∠3 & ∠6 and ∠4 & ∠5 are the examples of Alternate Interior Angles.

Note: Angles ∠3 and ∠5, ∠4 and ∠6, ∠1 and ∠7, and ∠2 and ∠8 are Alternates Angles.

In geometry, alternate interior angles are special pairs of angles formed when a line, called a transversal, intersects two other lines. They sit on opposite sides of the transversal and inside the two other lines. When the lines being intersected are parallel, these angles are equal in measure.

In this article, we will discuss the concept of Alternate Interior Angles in detail including its definition, example, and properties. We will also learn about the Alternate Interior Angle Theorem and its converse and their proof as well.