irnsrgn Posted January 30, 2009 Posted January 30, 2009 To draw an ellipse you need to know the width AB in the drawing and the length CD in the drawing, You lay these out (draw them) on a piece of posterboard or other medium. Fig 1 You can use a piece of string tied together as in Fig 2 You use a pencil inside the string with the string around the 2 points P. To find these points P, there is a very complicated algebra formula, or you can just use a compass set the distance from where AB and CD cross in the middle to either C or D, then scribe an arc on either side of line AB using A as the common point to swing the arcs. Where these 2 arcs intersect line CD are points P. Using thumb tacks sticking out from the front side at both points P and point A, tie the string so it is tight around these 3 points. Fig 2 Remove the tack at point A, and using a pencil held tight against the inside of the string, draw the ellipse keeping the string taunt (tight) all the way around. Quote
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