The green blades form a bowtie that is symmetric about the vertical orange line g. Show that the blue horizontal line f, the red circle (ADE), and the purple circle (AOC) are concurrent. (Assume that COB and AOD are colinear.)

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## Solution

Note that the right angle was not used, so the result stays true without that constraint.

## One reply on “The whirligig”

The blue line need not be perpendicular to the orange dotted line, and the result is still true. This was discovered by Lewis Corner and his animation of the result.