# Definition:Tangent/Geometry/Tangent Line

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## Definition

In the words of Euclid:

*A straight line is said to***touch a circle**which, meeting the circle and being produced, does not cut the circle.

(*The Elements*: Book $\text{III}$: Definition $2$)

In the above diagram, the line is **tangent** to the circle at the point $C$.

## Sources

- 2014: Christopher Clapham and James Nicholson:
*The Concise Oxford Dictionary of Mathematics*(5th ed.) ... (previous) ... (next): Entry:**tangent**(to a curve)