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Angle sum of a triangle

Use parallel lines to prove the angles of a triangle add to 180°, then find unknown interior and exterior angles.

⏱ 18 min❓ 10 questions

What you'll be able to do

  • ✔I can explain why the angles in a triangle add to 180°
  • ✔I can find an unknown angle in a triangle
  • ✔I can use the exterior angle of a triangle to find unknown angles

How this works

  1. 1Read the short explanations first — they teach you what you need before each question.
  2. 2Answer each question, then tap Check. A right answer moves you on automatically; if it's wrong, you'll see a friendly explanation of why.
  3. 3Finish all 3 steps to see your score — sign in and subscribe to unlock the full lesson and save it.

What's inside

10 questions and 1 quick teaching card, including:

  • 🔢Number answer — Work out the answer and type the number.

👪Grown-up tip: sit alongside younger learners for the first few lessons. Read the questions together and chat about the explanations — that's where the real learning sticks.

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Curriculum: AC9M7M05