Mon Prof Augmenté
Three corners make a straight line
Age 12 · Maths
If you tear the three corners off any paper triangle and put their tips together, they fit perfectly along a straight edge. That shows the three angles of a triangle always add up to 180°, a straight angle.
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In the picture
- Red corner: the first angle of the triangle
- Yellow corner: the second angle of the triangle
- Blue corner: the third angle of the triangle
- The ruler’s straight edge: the three angles together make a straight angle, 180°
Examples
- A slice of pizza cut into a triangle: its three corner angles still add up to 180°.
- A triangular road sign: however big it is, its three angles add up to 180°.
Key takeaways
- In every triangle, the three angles add up to 180°.
- If you know two angles, you can find the third by subtracting them from 180°.
Quiz: Three corners make a straight line (Age 12)
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In any triangle, what do the three angles add up to?
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A triangle has two angles of 50° and 70°. How big is the third angle?
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If you tear the three corners off a paper triangle and put their tips together, what shape do they make?
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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