Lesson 7 of 15
Will these three close?
Show on a big screenA shop cuts kite sticks: 2 cm, 4 cm and 7 cm. The two shorter sticks cannot reach across the longest stick.
Step 1 of 3
- The longest stick, 10, lies flat as a base.
- Sticks of 6 and 8 swing up from its ends and cross. It closes.
- A base of 7, with sticks of 2 and 4. They cannot reach.
Each length must be less than the other two added
Lay the longest stick flat as the base, the bottom side. Swing the other two sticks up from its ends. If they cross, they make the third corner.
The triangle inequality: each length is less than the other two added. When this is true, a triangle exists.
| Lengths | Two shorter add to | Longest | Closes? |
|---|---|---|---|
| 6, 8, 10 | 14 | 10 | Yes. 14 is more than 10 |
| 5, 12, 13 | 17 | 13 | Yes. 17 is more than 13 |
| 2, 3, 5 | 5 | 5 | No. Only equal |
| 2, 4, 7 | 6 | 7 | No. Too short |
For 2, 3 and 5 the sticks lie in a flat line. So they make no triangle.
Tap Next set. Guess. Then swing the sticks.
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