ARGAND DIAGRAM

graphic portrayal of complex numbers, those of the form a + bi, in which a and b are real numbers and i is the square root of -1; it was devised by the Swiss mathematician Jean Robert Argand in about 1806. One axis represents the pure imaginary numbers (those consisting of the bi portion only); the second represents the real numbers (a values only). This permits the complex numbers to be plotted as points in the field defined by the two axes.