Geometry for Elementary School/Our tools: Ruler and compass

How to draw a line


We will use the notation $$\overline{AB}$$ for the line segment the starts at A and ends at B. Note that we don't care about the segment direction and therefore $$\overline{AB}$$ is the same as $$\overline{BA}$$.



How to draw a circle

 * Using the compass (based on Book I, Postulate 3).

We use the notation $$\circ A,\overline{AB} $$ for the circle whose centre is the point A and its radius length equals that of the segment $$\overline{AB}$$.



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.

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