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Math Forum » Discussions » Math Topics » geometry.pre-college.independent

Topic: Semicircles
Replies: 3   Last Post: Jul 27, 1994 12:17 PM

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Pao-Ping Lin

Posts: 2
Registered: 12/6/04
Re: Semicircles
Posted: Jul 26, 1994 6:01 PM
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In article <heather-250794103122@erewhon.swarthmore.edu> Heather
Mateyak,
heather@forum.swarthmore.edu writes:
>Does anyone know how to draw a semicircle using Sketchpad? If this
>question has been asked before, pardon my ignorance.
>


Actually, you can draw any curve you want just by plotting points on a
pre-determined coordinate system ( two lines which can be moved by
dragging the intersection point), connecting those points by segments
and then hide the axes or other elements you do not want. A semicircle
is even easier. Draw a circle and one of it diameter. Equally divide half
of the circle by rotating an end point of the diameter about the center.
Connecting those points with segments and hiding the original circle,
you get a semicircle. If you are worrying about the smoothness of the
curve get more points and use a big circle to start. If you begin with two
free point and use the midpoint as center of the desired circle you obtain
a semicircle with variable diameter. Its defining elements are the two free
points. Of course, any curve constructed this way is not an object like
circle or line on GSP. You can not get a real "variable" point on it. But
you can use point on the original circle. It can trace the semicircle but not
limit by the semicircle.


Pao-Ping Lin, Ph. D.
1, Ai-Kuo West Road
Taipei Municipal Teachers College
Department of Mathematics and Science Education
Taipei, Taiwan, R. O. C.

E-mail: Unit760@twnmoe10.edu.tw
Fax : (02) 389-7641
Phone: (O) (02) 3113040 ext 1901
(H) (02) 726-8523






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