Geometry · Points, Lines & Angles
Supplementary Angles
HSG-CO.A.1
Definition
Two angles whose measures have a sum of 180 degrees.
Examples
- 110 degrees and 70 degrees are supplementary because 110 + 70 = 180.
- 150 degrees and 30 degrees are supplementary because 150 + 30 = 180.
Key rule
Supplementary angles always add up to exactly 180 degrees.
Memory hook
'S' for supplementary, 's' for straight — they add to 180 degrees.