- Definition
Complementary angles are two angles that, when added together, make a perfect right angle (90 degrees).
If a right angle is split into two smaller angles, one measuring 40°, its complementary angle must be 50° because 40 + 50 = 90.
How to teach this in 30 seconds
Try this analogy: Complementary angles are like two puzzle pieces that fit together perfectly to make a square corner.
Ask your child: If one angle is 60°, what's the other angle that makes a perfect corner?
Common mix-up: Kids often mix up complementary (90°) and supplementary (180°) angles. A good trick is 'C' for Corner (90°) and 'S' for Straight line (180°).
Examples
- A 25° angle and a 65° angle are complementary.
- The corner of a picture frame is a 90° angle, so if a line splits it, the two new angles are complementary.
complementary angles is a term used in Ontario’s Kindergarten to Grade 8 curriculum.
Where this shows up
The descriptions on this page are SmartStudy’s own original, plain-language writing — not the Ministry’s wording. They are aligned to the Ontario Curriculum, © King’s Printer for Ontario. For the Ministry’s official wording, see the source link below. SmartStudy is an independent service and is not affiliated with, endorsed by, or sponsored by the Government of Ontario or the Ministry of Education. Ontario Curriculum and Resources ↗
