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The circles and with centers and do not intersect. Draw the tangents from to and from to . The chords and , shown in red, are equal in length.
Contributed by: Izidor Hafner (December 2018)
Open content licensed under CC BY-NC-SA
Let , , .
Then , .
 D. Wells, The Penguin Dictionary of Curious and Interesting Geometry, New York: Penguin Books, 1991 p. 70.