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Re: Semicircles
Posted:
Jul 26, 1994 6:01 PM


In article <heather250794103122@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 predetermined 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.
PaoPing Lin, Ph. D. 1, AiKuo West Road Taipei Municipal Teachers College Department of Mathematics and Science Education Taipei, Taiwan, R. O. C.
Email: Unit760@twnmoe10.edu.tw Fax : (02) 3897641 Phone: (O) (02) 3113040 ext 1901 (H) (02) 7268523



