# Geometry for Elementary School/Our tools: Ruler and compass

 Geometry for Elementary School Construction Our Tools: Ruler and compasses Constructing equilateral triangle

## How to draw a line

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

## How to draw a circle

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

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.