hy·po·cy·cloid /ˌhaɪpoˈsaɪˌklɔɪd/
次擺圓; 圓內旋輪線
Hy·po·cy·cloid n. Geom. A curve traced by a point in the circumference of a circle which rolls on the concave side in the fixed circle. Cf. Epicycloid, and Trochoid.
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hypocycloid
n : a line generated by a point on a circle that rolls around
inside another circle