Angle sums in triangles and polygons
Derive and use the angle sum in a triangle (180°), use it to deduce the angle sum in any polygon ((n−2) × 180°), and calculate interior and exterior angles of regular polygons
Teaching approaches
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1 approach
If your child knows two angles of a triangle are 50° and 70°, can they work out the third? And can they figure out the angles inside a regular pentagon?
Derive and use the angle sum in a triangle (180°), use it to deduce the angle sum in any polygon ((n−2) × 180°), and calculate interior and exterior angles of regular polygons
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3 before · 1 after
Before
This concept
Check understanding
- Calculate a missing angle in a triangle by subtracting the known angles from 180°
- Find the sum of interior angles in a hexagon by dividing it into triangles
- Calculate each interior and exterior angle of a regular polygon given the number of sides
“If your child knows two angles of a triangle are 50° and 70°, can they work out the third? And can they figure out the angles inside a regular pentagon?”
Curriculum record
- Type
- Procedural
- Subject
- Mathematics
- Domain
- Geometry
- Age range
- Ages 11–14
Standards