Lesson 1 of 16
Landing one on the other
Show on a big screenSlide one tiffin lid onto the other. No gap anywhere. You may slide, turn or flip the copy. A copy that fits exactly on top has landed on it.
Drag the slider. Watch the copy move onto the grey shape.
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Step 1 of 4
- A copy sits apart from the grey target.
- Slide it, and turn it, toward the target.
- It lands exactly on the target. No gaps.
- Every side now carries a matching tick mark.
The test for twins
Two figures are congruent when one lands exactly on the other. They have the same shape and the same size.
Every corner sits on a corner. Every side sits on a side.
| Question | What it tells you |
|---|---|
| Do they look the same? | Not enough. |
| Does one land exactly on the other? | Yes means congruent. |
| Is there still a gap after every slide, turn and flip? | Yes means not congruent. |
Example: one triangle has sides 5, 6 and 7 cm. Another has sides 5, 6 and 8 cm. The longest sides are 7 cm and 8 cm. They differ by 8 − 7 = 1 cm. So the triangles cannot land.
Try the lab to finish this lesson.