Angles in triangles (age 10+)
Find unknown angles in triangles, quadrilaterals, and regular polygons using angle sum properties
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“If your child knows that angles in a triangle always add up to 180°, and two angles in a triangle are 55° and 70°, can they work out the third angle without measuring it?”
Full guide and materials
- Activity. Find unknown angles in triangles, quadrilaterals, and regular polygons using angle sum properties
What to notice. Find a missing angle in a triangle given two angles (using angle sum = 180°) • Calculate a missing angle in a quadrilateral (angle sum = 360°) • Calculate the interior angle of a regular hexagon from the angle sum formula
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If your child knows that angles in a triangle always add up to 180°, and two angles in a triangle are 55° and 70°, can they work out the third angle without measuring it?
Find unknown angles in triangles, quadrilaterals, and regular polygons using angle sum properties
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- Find a missing angle in a triangle given two angles (using angle sum = 180°)
- Calculate a missing angle in a quadrilateral (angle sum = 360°)
- Calculate the interior angle of a regular hexagon from the angle sum formula
“If your child knows that angles in a triangle always add up to 180°, and two angles in a triangle are 55° and 70°, can they work out the third angle without measuring it?”
Curriculum record
- Type
- Procedural
- Subject
- Mathematics
- Domain
- Geometry
- Age range
- Ages 10–11