Lesson 1 of 9
Exact, not neat
Show on a big screenA figure can look right and still be wrong. A ruler shows a length in millimetres.
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The rule
A construction is a figure drawn with a ruler and compass. Its lengths come from exact steps.
Check it with numbers. Every side the same means it passes. One side different means it only looks right.
Step 1 of 4
- A compass has two legs, joined at the top.
- One leg ends in a sharp point.
- The other leg holds a pencil.
- The gap between them is the span.
The compass point is sharp. So put it gently on the paper.
Example
A four-sided figure has sides 45, 45, 45 and 45 mm. The mm means millimetres. All sides are the same, so the figure passes.
Another has sides 40, 40, 40 and 42 mm. They are not all the same, so it only looks right.
Watch out!
Four equal sides do not always make a square. A square also needs four square corners.
Try the lab to finish this lesson.