Euclid's Elements Book I

23 definitions · 5 postulates · 5 common notions · 48 propositions

Compass and straightedge

Only a straightedge and a compass. See what you can construct.

How it works

  • Segment and line: click two points (Postulates 1 and 2).
  • Circle: click the centre, then a point on the circle (Postulate 3).
  • Near the crossing of two lines a red ring appears; click it to take the intersection. Drag the original points and the intersection follows.
  • With the Move tool you can drag the free points.

Try this

  • Construct an equilateral triangle on AB (I.1).
  • Bisect the segment AB (I.10).
  • Draw a perpendicular from a point on AB (I.11).