**Cartesian equation: **

*y* = *mx* + *c*

**or parametrically: **

*x* = *at* + *b*, *y* = *ct* +*d*

**Click below to see one of the Associated curves.**

Click THIS LINK to experiment interactively with this curve and its associated curves.

The straight line must be one of the earliest curves studied, but Euclid in his

In fact nobody attempted a general definition of a curve until Jordan in his *Cours d'Analyse*in 1893.

The inverse of a straight line is a circle if the centre of inversion is not on the line.

The negative pedal of the straight line is a parabola if the pedal point is not on the line.

Since normals to a straight line never intersect and tangents coincide with the curve, evolutes, involutes and pedal curves are not too interesting.

**Other Web site:**

Jeff Miller (Why is the slope of a straight line called *m*?)

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JOC/EFR/BS January 1997

The URL of this page is:

http://www-history.mcs.st-andrews.ac.uk/Curves/Straight.html