a closed plane curve resulting from the intersection of a circular cone and a plane cutting completely through it; "the sums of the distances from the foci to any point on an ellipse is constant" 円錐と、円錐を完全に横断する平面との交差によってできる平面の閉曲線。
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【下位】 ellipse in which the two axes are of equal length; a plane curve generated by one point moving at a constant distance from a fixed point; "he calculated the circumference of the circle" 2本の軸が等しい長さである楕円。固定した1点から一定の距離で動く1点の作る平面曲線。
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