Geometry · Parallel Lines & Angle Pairs
Alternate Interior Angles
HSG-CO.C.9
Definition
Congruent angles between 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
- 65 = 65 degrees for a pair of alternate interior angles on parallel lines.
- Alternate interior angles form a 'Z' pattern between the two lines.
Key rule
Alternate interior angles are congruent only when the lines are parallel.
Memory hook
Inside the lines, opposite sides — the 'Z' pattern.