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[kahr-dee-oid] /ˈkɑr diˌɔɪd/
noun, Mathematics.
a somewhat heart-shaped curve, being the path of a point on a circle that rolls externally, without slipping, on another equal circle. Equation: r = a (1−cosA).
Origin of cardioid
First recorded in 1745-55, cardioid is from the Greek word kardioeidḗs heart-shaped. See cardi-, -oid Unabridged
Based on the Random House Dictionary, © Random House, Inc. 2017.
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British Dictionary definitions for cardioid


a heart-shaped curve generated by a fixed point on a circle as it rolls around another fixed circle of equal radius, a. Equation: r = a(1 – cos φ), where r is the radius vector and φ is the polar angle
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition
© William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins
Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012
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cardioid in Science
A heart-shaped plane curve, the locus of a fixed point on a circle that rolls on the circumference of another circle with the same radius.
The American Heritage® Science Dictionary
Copyright © 2002. Published by Houghton Mifflin. All rights reserved.
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