Mack's Square Root Extractor

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This Demonstration presents T. R. Mack's square root extractor [1]. Choose a number on the horizontal scale, then turn the red ruler until the same number lies directly above the chosen number. Then the square root is directly to the left on the vertical scale.

Contributed by: Izidor Hafner (September 2012)
Open content licensed under CC BY-NC-SA



The extractor is based on the Pythagorean theorem: , so .


[1] L. A. Graham, Ingenious Mathematical Problems and Methods, New York: Dover Publications, 1959 pp. 73–74.

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