ABSTRACT

Although it is not an ordinary or real number, the square root of minus one has such useful properties that its use is unavoidable and has given rise to the branch of mathematics known as complex variables. This unusual number has come to be known as i, the imaginary unit, the basis of complex numbers. This entry explains why complex numbers are no more “imaginary” than the infinite decimal, and it discusses why the mathematics of complex variables is an essential part of modern mathematics.