# Understanding Transversal and Parallel Lines Relationship

## Is it true that if a transversal intersect two parallel lines, then it is perpendicular?

It seems like there is a confusion with the relationship between transversal and parallel lines. Let's clarify the concept. If a transversal intersects two lines so that corresponding angles are congruent, then the lines are parallel. On the other hand, if a transversal intersects two lines so that interior angles on the same side of the transversal are supplementary, then the lines are also parallel.

## Understanding Transversal and Parallel Lines Relationship

**Transversal:** In geometry, a transversal is a line that intersects two or more lines at distinct points. When a transversal intersects two parallel lines, interesting properties and relationships emerge.

## Corresponding Angles

**Corresponding angles:** Corresponding angles are angles that occupy the same relative position at each intersection where a transversal intersects two lines. When two lines are parallel, corresponding angles are congruent (equal in measure).

For example, in the figure below:

∠1 and ∠5 are corresponding angles, and they are congruent because the lines are parallel. Similarly, ∠2 and ∠6, as well as ∠3 and ∠7, are also corresponding angles that are congruent due to the parallel lines relationship.

## Interior Angles on the Same Side of the Transversal

**Interior angles:** Interior angles are the angles between two lines when a third line (transversal) intersects them. When a transversal intersects two parallel lines, the interior angles on the same side of the transversal are supplementary (their measures add up to 180 degrees).

For instance, in the figure below:

∠3 and ∠5 are interior angles on the same side of the transversal. Since the lines are parallel, these angles are supplementary, which means ∠3 + ∠5 = 180 degrees. Similarly, ∠4 and ∠6 are also supplementary due to the parallel lines relationship.

Thus, if a transversal intersects two parallel lines so that corresponding angles are congruent or interior angles on the same side of the transversal are supplementary, then we can conclude that the lines are indeed parallel, not perpendicular. It's crucial to understand these fundamental properties when working with transversals and parallel lines in geometry.