Angles in triangles (age 10+)
Find unknown angles in triangles, quadrilaterals, and regular polygons using angle sum properties
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1858 concepts · 9 subjects
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Angles in triangles (age 10+) means practising the idea at the table with counters or paper models and one clear check. We will demo once, then your child tries.
Materials: 20 counters or beans; Paper and pencil for recording sums. Adult models 7 + 5 with counters, then writes the sum. Child builds three addition problems with counters and records each sum. Done: three correct sums with counters matching the written numbers. Stop after the fresh check; keep optional challenge for another day.
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Learning resources
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PhET Interactive Simulations · Practice link — not the full lesson
Area Builder
Before you open · source notes
Area Builder supports hands-on exploration for Angles in triangles (age 10+). Not every lab worksheet.
Free interactive page, no sign-in required for the tested path.
Before you openAsk the learner what they changed in the sim or page and what they observed.
Opening this link does not save learning or assess mastery.
Source, access and review notes
Public PhET Interactive Simulations page. An anonymous GET on 2026-11-12 returned HTTP 200 with no login or payment prompt for this URL. Opening the link does not save practice or assess mastery. An adult should preview and guide the learner.
PhET Interactive Simulations. “Area Builder.” External page; Gakuva does not copy, host, embed, or redistribute materials.
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Check understanding
- 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 10–12
Standards