conchoid
柯林斯词典
1. N a plane curve consisting of two branches situated about a line to which they are asymptotic, so that a line from a fixed point (the pole) intersecting both branches is of constant length between asymptote and either branch. Equation: (x – a)²(x² + y²) = b²x² where a is the distance between the pole and a vertical asymptote and b is the length of the constant segment 蚌线[geometry]
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