Angle Sum of a Triangle

The three interior angles of a triangle fit together into a straight line: 180°

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About This Practice

Tear the three angles off any triangle and place them side by side: they exactly fill a straight line — a straight angle of 180°. So the interior angles of every triangle always add up to 180°, big or small, skinny or wide.

A random triangle appears — tap its three corners to tear the angles off and lay them along a straight line. They exactly fill a straight angle. Try new triangles and discover the sum is always 180°.

EasyEstimated Time: 10mintriangleangle sumstraight angle180 degrees

How to Play

  1. Read the three angles and guess their sum first.
  2. Tap the corners one by one to tear the angles off.
  3. Watch the sectors fill the line: what do they form? (a straight angle)
  4. Check the sentence: the three angles add up to exactly 180°.
  5. Tap “New One” to test more triangles and confirm the rule.

Learning Objectives

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