An Argand diagram is a way of representing complex
numbers as points on a coordinate plane, also known as the Argand
plane or the complex plane, using the x-axis
as the real axis and the y-axis as the imaginary axis. It is named
for the French amateur mathematician Jean Robert Argand (1768–1822)
who described it in a paper in 1806.1 A similar method had been
suggested 120 years earlier by John Wallis and had been developed extensively by Casper Wessel.
But Wessel's paper was published in Danish and wasn't circulated in the
languages more common to mathematics at that time. In fact, it wasn't until
1895 that his paper came to the attention of the mathematical community
– long after the name "Argand diagram" had stuck.
In the diagram shown here, a complex number z is shown in terms of
both Cartesian (x, y) and polar (r, θ)
- Argand, R. Essai sur une manière de représenter les quantités
imaginaires dans les constructions géométriques. Paris: Albert
Blanchard, 1971. Reprint of the 2nd ed., published by G. J. Hoel in
1874. First edition published Paris, 1806.