Angles in triangles (age 10+)
Find unknown angles in triangles, quadrilaterals, and regular polygons using angle sum properties
Lesson
Set out your lesson
“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.”
Bring to the table
- 20 counters or beans
- Paper and pencil for recording sums
Extra for the adult
Worked example. 7 counters plus 5 counters make 12. Write 7 + 5 = 12.
Optional challenge. For Angles in triangles (age 10+), add one harder example after success.
What to notice. Keep one parent note: examples tried; results; support used. This session samples Angles in triangles (age 10+), not mastery.
Share and support
Family records and proof options
Keep a record of your learning
Save photos, notes, and attendance. Export a proof packet for compliance or portfolio reviews.
Practice this concept
Start practiceAngles in triangles (age 10+) practice
Practice key ideas from Angles in triangles (age 10+).
Free · no login · no ads · Practice answers and completion are not saved. Parent observation remains the lesson record.
Learning resources
Extra practice links — they do not replace Gakuva’s teaching approach.
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.
Unknown — link only
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