半はん直ちょく線せん

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Meanings

1

noun

half line; ray

mathematics

Mathematical term for a line that starts at a point and extends infinitely in one direction.

直ちょく線せん
直線 is a straight line extending infinitely in both directions, while 半直線 starts at a point and extends infinitely in only one direction.
線せん分ぶん
線分 is a line segment with two endpoints, whereas 半直線 has one endpoint and extends infinitely.

Compound of 半 (half) and 直線 (straight line), reflecting the geometric concept of a half-line.