Proving lines parallel

Math

Definition

Methods to prove two lines are parallel using angle relationships formed by a transversal. If corresponding angles are equal, alternate interior angles are equal, or co-interior angles are supplementary, the lines are parallel.

Examples

  • If alternate interior angles measure 55° each, the lines are parallel
  • If corresponding angles are both 110°, the lines are parallel
  • If co-interior (same-side interior) angles sum to 180°, the lines are parallel

Related Terms

Angle pairs Parallel and perpendicular lines Two-column proofs Conditional statements

Study This Concept

Practice proving lines parallel with free review games in these units:

Geometry Unit 3: Parallel and Perpendicular Lines