二に等とう分ぶん線せん

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Meanings

bisector

A geometric term for a line that divides an angle or segment into two equal parts. Used in mathematics contexts.

垂すい直ちょく二に等とう分ぶん線せん
Specifically a perpendicular bisector, whereas 二等分線 can refer to any bisector (angle or segment).
角かくの二に等とう分ぶん線せん
Explicitly an angle bisector; 二等分線 alone is broader and can also refer to a segment bisector.

二に等とう分ぶん線せん
Standard kanji spelling for the geometric term 'bisector'.
２に等とう分ぶん線せん
Variant spelling using the numeral 2; less common but still encountered.

Compound of 二等分 (に等分, 'dividing into two equal parts') + 線 (せん, 'line'). The term is a straightforward mathematical coinage.