How do you know if two line segments are parallel?

Parallel lines never cut (intersect) or meet each other, and they lie on the same plane.

Answer: If any pair of corresponding angles, alternate interior angles, alternate exterior angles are equal or consecutive interior angles are supplementary, then two line segments are parallel

Parallel lines have the same slope on a coordinate plane.

Explanation:

Two lines will be parallel if any one of the followings conditions is fulfilled.

1. Any pair of corresponding angles are equal.

2. Any pair of alternate interior angles are equal.

3. Any pair of alternate exterior angles are equal.

4. Consecutive interior angles (co-interior) angles are supplementary.

Thus, If any pair of corresponding angles, alternate interior angles, alternate exterior angles are equal or consecutive interior angles are supplementary, then two line segments are parallel.