### tangent

• n. [数] 切线，[数] 正切
• n. (Tangent)人名；(瑞典)坦根特
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tangent 正切，切线

1590s, "meeting at a point without intersecting," from Latin tangentem (nominative tangens), present participle of tangere "to touch," from PIE root *tag- "to touch, to handle; border on; taste, partake of; strike, hit;" figuratively "affect, impress; trick, cheat; mention, speak of" (cognates: Latin tactus "touch;" Greek tassein "to arrange," tetagon "having seized;" Old English þaccian "stroke, strike gently"). First used by Danish mathematician Thomas Fincke in "Geomietria Rotundi" (1583). Extended sense of "slightly connected with a subject" is first recorded 1825. Related: Tangence; tangency.
tangent (n.)
1590s as a geometric function, from tangent (adj.). From 1650s as "a tangent line." Figurative use of off on a tangent is from 1771.
1. The conversation went off at a tangent.

2. The graph of a concave function is always below its tangent.

3. The tangent may be used to find the direction.

4. For? 0 we naturally get a circle; for? 0 we obtain two tangent circles.

5. It's not easy to follow her thought because she's always going off at a tangent.