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

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## Introduction

[edit | edit source]## How to draw a line

[edit | edit source]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 .

## 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 .

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.