Geometry · Points, Lines & Angles
Complementary Angles
HSG-CO.A.1
Definition
Two angles whose measures have a sum of 90 degrees.
Examples
- 60 degrees and 30 degrees are complementary because 60 + 30 = 90.
- 20 degrees and 70 degrees are complementary because 20 + 70 = 90.
Key rule
Complementary angles always add up to exactly 90 degrees.
Memory hook
'C' for complementary, 'c' for corner — they add to 90 degrees.