2013년 10월 24일 목요일

Mascheroni Construction

A geometric construction done with a movable compass alone. All constructions possible with a compass and straightedge are possible with a movable compass alone, as was proved by Mascheroni (1797). Mascheroni's results are now known to have been anticipated largely by Mohr (1672).
MascheroniMidpoint
An example of a Mascheroni construction of the midpoint M of a line segment specified by two points A and B illustrated above (Steinhaus 1999, Wells 1991). Without loss of generality, take AB=1.

1. Construct circles centered at A and B passing through B and A. These are unit circles centered at (0, 0) and (1, 0).

2. Locate C, the indicated intersection of circles A and B, and draw a circle centered on C passing through points A and B. This circle has center (1/2, sqrt(3)/2) and radius 1.

3. Locate D, the indicated intersection of circles B and C, and draw a circle centered on C passing through points B and C. This circle has center (3/2, sqrt(3)/2) and radius 1.

4. Locate E, the indicated intersection of circles B and D, and draw a circle centered on E passing through point C. This circle has center (2, 0) and radius sqrt(3).

5. Locate F and G, the intersections of circles AE and EC. These points are located at positions (5/4, +/-sqrt(39)/4).

6. Locate M, the intersection of circles F and G. This point has position (1/2, 0), and is therefore the desired midpoint of AB^_.

Pedoe (1995, pp. xviii-xix) also gives a Mascheroni solution.
Wolfram

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