Geometry for Elementary School/Our tools: Ruler and compass
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Introduction
[edit | edit source]![](http://upload.wikimedia.org/wikipedia/commons/thumb/3/32/Geom_compass_ruler.png/300px-Geom_compass_ruler.png)
How to draw a line
[edit | edit source]![](http://upload.wikimedia.org/wikipedia/commons/thumb/2/22/Geom_draw_line.png/300px-Geom_draw_line.png)
We will use the notation for the line segment the starts at A and ends at B. Note that we don't care about the segment direction and therefore is the same as .
![](http://upload.wikimedia.org/wikipedia/commons/thumb/a/a0/Geom_line_ab.png/300px-Geom_line_ab.png)
![](http://upload.wikimedia.org/wikipedia/commons/thumb/7/73/Geom_line_ba.png/300px-Geom_line_ba.png)
How to draw a circle
[edit | edit source]- Using the compass (based on Book I, Postulate 3).
We use the notation for the circle whose centre is the point A and its radius length equals that of the segment .
![](http://upload.wikimedia.org/wikipedia/commons/thumb/7/7d/Geom_draw_circle_sequence.png/300px-Geom_draw_circle_sequence.png)
Note that in other sources, such as Euclid's Elements, a circle is described by any 3 points on its circumference, ABC.
The center-radius notation was chosen because of its suitability for constructing circles with a ruler and a compass.