⎯⎯ Parallel Lines and Transversals

Parallel Lines

Two lines in the same plane that never intersect are parallel (symbol: ∥). When a third line called a transversal crosses two parallel lines, it creates 8 angles with predictable relationships.

Angle Pair Theorems

• Corresponding angles: same position at each intersection — congruent (∥ lines)
• Alternate interior angles: between the lines, on opposite sides — congruent (∥ lines)
• Alternate exterior angles: outside the lines, on opposite sides — congruent (∥ lines)
• Co-interior (same-side interior): between the lines, same side — supplementary (sum 180°)