Complex number

A complex number is a number that can be expressed in the form a + bi, where a and b are real numbers and i is the imaginary unit, where i² = −1.^[1]In this expression, a is the real part and b is the imaginary part of the complex number. Complex numbers extend the idea of the one-dimensionalnumber line to the two-dimensional complex plane by using the horizontal axis for the real part and the vertical axis for the imaginary part. The complex number a + bi can be identified with the point (a, b) in the complex plane. A complex number whose real part is zero is said to be purely imaginary, whereas a complex number whose imaginary part is zero is a real number. In this way the complex numbers contain the ordinary real numbers while extending them in order to solve problems that cannot be solved with real numbers alone.

Complex numbers are used in many scientific and engineering fields, including physics, chemistry, biology, economics, electrical engineering,mathematics, and statistics. The Italian mathematician Gerolamo Cardano is the first known to have introduced complex numbers. He called them "fictitious" during his attempts to find solutions to cubic equations in the 16th century,^[2] but complex numbers are no more or less "fictitious" or "imaginary" than any other kind of number.