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The three angles of any triangle add up to 180°. If one side is extended, the exterior angle equals the sum of the two interior angles opposite it. In an isosceles triangle two angles are equal. In a right-angled triangle, Pythagoras says longest side² = sum of the squares of the other two sides. And three lengths make a triangle only if the two shorter ones add up to more than the longest.
✓ You passed this lesson’s test.
Inside 180, outside the sum — “the angles add up to 180°; an exterior angle equals the two opposite interior angles”
Use it for: Roof frames, ladders against walls, shortcuts across a field, and the triangles chapter of Class 7 maths.
Check: 45 + 65 = 110 ✓, and the third angle 180 − 110 = 70 makes 45 + 65 + 70 = 180 ✓
▶ Watch it animatedWork it out in your head or on paper, type the answer and press Check. Stuck? Press “Show me how”.
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20 sums. Check each answer, then go to the next one. Get 16 or more right to pass.
🏅 Sign in with Google to earn the 🔻 Triangle Tamer badge when you pass — and a certificate when you finish all 8 lessons of Part 7 · Class 7. You can still take the test without signing in.
Why does it work? When should you use it? Ask in English, मराठी or हिंदी.
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