英语释义
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n. A certain conic section supposed to be drawn in the
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tangent plane to any surface, and used to determine the accidents of
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curvature of the surface at the point of contact. The curve is similar
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to the intersection of the surface with a parallel to the tangent plane
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and indefinitely near it. It is an ellipse when the curvature is
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synclastic, and an hyperbola when the curvature is anticlastic.