Idea 15of 24Builds onEvery triangle has three anglesA degree is a tiny turn
A triangle's angles make 180°
What do the three angles of any triangle add up to?
Today you'll discover
- a way to add angles without numbers
- the total for every triangle
- why the shape does not matter
Think firstAngles of 50°, 70° and 60°
Tear off the three corners and lay them side by side. What will they make?
Decide first, then press Next. Watch the three coloured corners line up.
A triangle with angles 50°, 70° and 60°, each corner shaded its own colour. The corners are torn off, then slide and turn until they sit side by side at one point on a flat line on the right, filling it exactly. A sentence across the top reads 50° + 70° + 60° = 180°. Then a wide triangle, 30°, 40° and 110°, does the same. The last step shows a long, flat triangle.
See the whole ideathe big idea and the key word, in one place
The big idea
The three angles of every triangle add up to 180°, a straight line.
Why it worksTorn off and laid side by side, the three corners always fill a straight line, and a straight line is 180°.
Easy to get wrongMeasured angles can be a degree off. If yours add to 179° or 181°, measure again; the true total is 180°.
Key word
- angle sum
- the total of all the angles inside a shape; for a triangle it is 180°
Ready to use it?
- Check that a triangle's angles add to 180°.
- Decide whether three angles can make a triangle.