8th Grade · Geometry
Co-Interior Angles
8.G.A.5
Definition
A pair of angles between two lines and on the same side of a transversal. When the lines are parallel, these angles are supplementary, summing to 180 degrees.
Teach it
Where it is taught, with guided notes, practice, homework, an exit ticket and an interactive Teacher Deck.
Examples
- If one co-interior angle is 110°, the other is 70° (110+70 = 180).
- Also called same-side interior angles.
Key rule
Co-interior angles are supplementary — they add to 180°.
Memory hook
Same side, inside the lines, add to 180°.