Geometry · Parallel Lines & Angle Pairs
Alternate Exterior Angles
HSG-CO.C.9
Definition
Congruent angles outside two parallel lines on opposite sides of the transversal.
Teach it
Where it is taught, with guided notes, practice, homework, an exit ticket and an interactive Teacher Deck.
Examples
- 115 = 115 degrees for a pair of alternate exterior angles on parallel lines.
- Alternate exterior angles sit above and below both parallel lines, on opposite sides of the transversal.
Key rule
Alternate exterior angles are congruent only when the lines are parallel.
Memory hook
Outside the lines, opposite sides.