Mon Prof Augmenté
Three corners on a ruler edge
Age 12 · Maths
Take the three corners of any paper triangle and lay them side by side on a straight edge. Together they fill exactly a straight angle, so the three angles of a triangle add up to 180°.
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In the picture
- Red corner of the paper triangle: the first of the three angles
- Blue corner of the paper triangle: the second angle
- Yellow corner of the paper triangle: the third angle
- Point where the three torn tips meet on the ruler edge: the three angles together fill a half-turn
Examples
- A triangular slice of pizza: its three corner angles always form a straight angle.
- A triangular road sign or a set square: however stretched it looks, its three angles fill a half-turn.
Key takeaways
- The three interior angles of any triangle add up to 180°.
- That sum is the same for every triangle, whatever its shape or size.
Quiz: Three corners on a ruler edge (Age 12)
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What do the three interior angles of any triangle add up to?
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What happens to the sum of the interior angles when a triangle is made larger?
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If two angles of a triangle are 50° and 60°, what is the third angle?
The answers, each with its explanation, are in the app. This lesson has left the free week, so its quiz is part of the subscription.
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