Euclid’s Tools

Circles, lines and an equilateral triangle

An interactive lesson with 6 steps, about 5 minutes: you predict, drag and solve, with instant feedback on every answer. It runs in your browser and needs JavaScript.

What you’ll learn

• Straightedge: a line through two points. Compass: a circle with a given centre through a given point.
• New points come only from intersections.
• An equilateral triangle comes from two circles of radius AB.

Steps

1. Only two moves
2. Euclid’s first construction
3. How tall is it?
4. Copying a length
5. Where the circles cross
6. Throw away the ruler?