- Definition
An exterior angle is formed when you extend one side of a shape, and it's the angle created outside the shape between that extended line and the next side.
If a triangle's interior angle is 60°, its exterior angle on the same straight line is 120°.
How to teach this in 30 seconds
Try this analogy: Imagine walking along the edge of a big play structure; the turn you make at each corner is like an exterior angle.
Ask your child: If you walked along the sides of this book, how much would you turn at the corner?
Common mix-up: Kids might confuse this with the interior angle. The exterior angle is the 'turn' you make on the outside when you extend one of the shape's sides straight past a corner.
Examples
- At each corner of a square, the interior angle is 90° and the exterior angle is also 90°.
- Imagine walking around a stop sign; the small turn you make at each corner is an exterior angle.
exterior angle 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 ↗
