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Discussion: All Tools in Geometry on Computer
Topic: geom construction software with compass -> arcs, not circles


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Subject:   geom construction software with compass -> arcs, not circles
Author: jdad
Date: Sep 22 2011
My son is taking geometry and has physical difficulty writing (he has a tremor),
so doing compass and straight edge constructions is very frustrating for him
even though he understands the principles.  I've been trying to find some
software for him to use, so he can create neat, accurate work with less
frustration.

I've purchase geometer's sketchpad, tried the Cabri demo, GeoGebra, Live
Geometry, Cinderella, and numerous others but I've consistently run into the
same problem.  When you use the compass, it creates a full circle.  If I'm doing
a construction like an inscribed octagon, the screen is littered with circles,
whereas the way you'd do it by hands just leaves the arc for the angle
bisections and perpendicular bisector.  My son balks at all the ink and doesn't
want his work to be different than the other kids.  Plus, it's hard to even find
the intersections among the maze of lines.

I've tried creating a custom tool in geometer's sketchpad by using the compass
and creating an arc on a circle and hiding the circle.  How to I create another
arc with the same radius though if I'm doing a perpendicular bisector?  Copy and
paste?  Then I can't seem to "flip" the arc and anchor it to the point at the
other end of the line segment.

The only thing I've found that draws arcs is this old, klunky java applet from
1997.   http://strader.cehd.tamu.edu/geometry/bisectangle1.0/bisectangle.html

Is there any full-featured geometry software (i.e., he can print, save, etc.)
with this sort of compass implementation?  I guess what I want is "arc by
radius" (a la "circle by radius").  I see tools for drawing arcs through 3
points, on a circle, and by center and two points, but not by center and radius
(and two points -- not necessarily on arc, but to give angle) as you'd use a
physical compass.

Any other software to try or features I'm missing in sketchpad, geogebra, and
company?

Thanks,
jdad

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