Read the epicycloid
is a kidney
-shaped plane algebraic curve
It is an epicycloid such that the outer of the two circle
s in the
definition of an epicycloid has radius
twice that of the other, a
An equation for the nephroid is (x2 + y2
- 4a2)3 = 108a4y2.
Like other epicycloids it finds applications in the study of gears.