To make an 11-gon, draw a diameter (the vertical line segment) and construct a perpendicular radius(AB). Draw a line segment from the midpoint to B (the longest diagonal line in the figure). Construct the midpoint of that line segment and use that point to point B as your circle radius. Move the compass around the circle, marking off this length. IF you've worked very carefully, the compass should meet point B with a very tiny gap. (This construction is not perfect).

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