Straightedge
Solve each geometric construction with compass and straightedge in as few moves as par allows, naming the theorem behind every line you draw.
How to play
Each puzzle gives you a few known points and a construction goal. Use the straightedge to draw lines and the compass to draw circles by clicking known points, tagging the theorem that justifies each move. New intersection points appear as you go; reach the goal in as few moves as possible.
- Pick the straightedge or compass tool and a theorem for the move
- Click one known point, then another, to draw a line or circle
- Intersections become new points you can build on
- Beat par on move count to score, and tag the right theorem each time
Game modes
- Daily: a fixed construction shared each day
- Practice: fresh randomized puzzles
- Compass-Only: solve using circles alone, with the straightedge forbidden
Controls
- Desktop: choose a tool and theorem, then click two known points to draw; Undo and Restart are available
- Phone & tablet: tap a tool, then tap two points to place each line or circle
Tips & strategy
- Plan the whole construction before drawing — overlapping circles of equal radius create the intersections that bisectors and perpendiculars need
- Every extra move past par costs score, so look for the most economical sequence rather than the first that works
What you'll learn
Straightedge is built on classical compass-and-straightedge construction, the geometry of the ancients.
- Skills: classical geometry, compass-and-straightedge construction, proof
- Best for: roughly grades 9–12 (ages 14+)
- For parents & teachers: classical compass-and-straightedge geometry.
About Straightedge
Straightedge is an original free browser geometry game built on classical compass-and-straightedge construction, rewarding elegant, minimal solutions and an understanding of the theorems that prove them.
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