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# Imaginary number

An imaginary number is a number whose square is negative. The term was coined by René Descartes in the seventeenth century and was meant to be derogatory: obviously such numbers don't exist. Nowadays we find the imaginary numbers on the vertical axis of the complex number plane. Every imaginary number can be written as [itex]ib[/itex] where [itex]b[/itex] is a real number and [itex]i[/itex] the imaginary unit with the property that

[itex]i^2 = -1.[/itex]
(In electrical engineering and related fields, the imaginary unit is often written as [itex]j[/itex] to avoid confusion with a changing current, traditionally denoted by [itex]i[/itex].) Every complex number can be written uniquely as a sum of a real number and an imaginary number.

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