📐 Angle Sum 📚 Grade 4 ⏱ 6 min
Triangle Angle Sum: A Tear-Off Experiment
A triangle's angles always add up to 180 degrees — this can be seen with your own eyes, not just memorized.
The tear-off experiment
Draw a triangle on paper. Tear off all three corners. Place them together, points touching at one spot — they form a straight line, meaning 180°.
💡 Why this works: a straight line is a flat angle of 180°. A triangle's three angles always combine into exactly that line, for any triangle.
Practice with known angles
Two angles of a triangle are 50° and 60°. What is the third? 180−50−60=70°.
FAQ
Does the rule work for every triangle?
Yes, the angle sum is always 180° — the same for acute, obtuse, and right triangles.