A syntractrix is a

curve In mathematics, a curve (also called a curved line in older texts) is an object similar to a line (geometry), line, but that does not have to be Linearity, straight. Intuitively, a curve may be thought of as the trace left by a moving point (ge ...

of the form :

x+\sqrt= a \ln \frac.

It is the locus of a point on the tangent of a tractrix at a constant distance from the point of tangency, as the point of tangency is moved along the curve. Dionysius Lardner, ''A system of algebraic geometry'' 1823, p. 261–26

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References

{{geometry-stub Plane curves