接せっ線せん

noun, noun which may take the genitive case particle 'no'

tangent line; tangential line

Geometry term for a line that touches a curve at exactly one point without crossing it.

• 円えんの接せっ線せんを引ひいてください。

  Please draw a tangent line to the circle.

• 曲きょく線せんの接せっ線せんの傾かたむきを求もとめる。

  Find the slope of the tangent line to the curve.