The cycloid was first studied by Nicholas of Cusa and later by Mersenne.
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The cycloid, epicycloids, and hypocycloids have the property that each is similar to its evolute.
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He announced that the curve required in the first problem must be a cycloid, and he gave a method of determining it.
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A cycloid is the curve traced by a point on the rim of a circular wheel as the wheel rolls along a straight line.
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Instead, the brachistochrone is a half cycloid, which was only proved much later with the development of calculus.
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In 1634 G.P. de Roberval showed that the area under one arch of a cycloid is three times the area of its generating circle.
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In 1658 Christopher Wren showed that the length of one arch of a cycloid is four times the diameter of its generating circle.
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A few years later, in 1659, Wallis published a tract containing the solution of the problems on the cycloid which had been proposed by Blaise Pascal.
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Torricelli extended this work to other curves such as the cycloid, and then the formula was generalized to fractional and negative powers by Wallis in 1656.
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More examples
A line generated by a point on a circle rolling along a straight line
Resembling a circle
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Smooth, with circular or concentric lines of growth (refers to fish scales).
Cycloid scales are thin, disk-like, and more or less circular, but not toothed, and are found on most soft-rayed bony fish;
In geometry, a curve resembling a series of arches traced out by a point on the circumference of a circle that rolls along a straight line. Its applications include the study of the motion of wheeled vehicles along roads and tracks.
Cycloid scales have a smooth outer edge, and are most common on more primitive fish with soft fin rays, such as salmon and carp.