单词	astroid
释义	astroid /ˈastrɔɪd / noun Mathematics A hypocycloid with four cusps (like a square with concave sides).The astroid was first discussed by Johann Bernoulli in 1691-92.... The caustic of the tricuspoid, where the rays are parallel and in any direction, is an astroid. The cycloidal curves, including the astroid, were discovered by Roemer (1674) in his search for the best form for gear teeth.
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