Idea 10of 24Builds onPut the protractor on the vertex
Every triangle has three angles
What does every triangle have, whatever its shape?
Today you'll discover
- the parts every triangle has
- where a triangle's angles are
- which side sits across from the biggest angle
Think firstTriangle ABC
This triangle has three sides. How many angles does it have inside it?
Decide first, then press Next. Count the corners, then read the lengths and the degrees.
A triangle with corners A, B and C. Its sides are then labelled 6 cm, 4 cm and 5 cm, and its corners 41°, 56° and 83°. Then a long, flat triangle with sides 7 cm, 3 cm and 5 cm and angles 22°, 38° and 120°; the 120° corner is ringed and the 7 cm side across from it drawn thick.
See the whole ideathe big idea and the key word, in one place
The big idea
Every triangle has three sides and three interior angles, one at each corner.
Why builders use trianglesA triangle's shape cannot change unless a side changes length. That is why bridges, roofs and bike frames are built from triangles.
Easy to get wrongThe angles of a triangle are the ones inside it. Measure the opening between the two sides at each corner.
Key words
- triangle
- a flat shape with three straight sides and three corners
- interior angle
- an angle inside a shape, between two sides at a corner
Ready to use it?
- Measure the sides and angles of a triangle.
- Find the side across from the biggest angle.