Idea 19of 24Builds onName a triangle by its sides
Build a triangle from three sides
How do you draw a triangle when you know its three sides?
Today you'll discover
- what to draw first
- how a compass finds the third corner
- how to check your triangle
Think firstBuild sides of 7 cm, 5 cm and 4 cm
The 7 cm base is drawn. Where is the third corner, C?
Decide first, then press Next. Watch where the two curves cross.
A 7 cm base from A to B. A compass arc of 5 cm is swung from A, then an arc of 4 cm from B; where they cross is marked C and joined to A and B. The last step shows a 6 cm base for a triangle with three 6 cm sides.
See the whole ideathe big idea and the key word, in one place
The big idea
Draw one side, then swing compass arcs with the other two lengths: they cross at the third corner.
Four stepsDraw the base. Open the compass to the second length; arc from one end. Open it to the third; arc from the other end. Join to the crossing.
No compass?Cut paper strips the length of the two sides. Pin one at each end of the base and swing them until their ends meet.
Key words
- compass
- a drawing tool with a point and a pencil, opened to a length to draw arcs and circles
- arc
- part of a circle; every point on it is the same distance from the centre
Ready to use it?
- Construct a triangle from three side lengths.