imaginary number

Also known as pure imaginary number, purely imaginary number

complex number that can be written as a real number multiplied by i

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An imaginary number is a type of number created by multiplying a real number by *i*, a special mathematical symbol that represents the square root of negative one. Imaginary numbers matter because they allow mathematicians and scientists to solve certain equations and describe phenomena that can't be handled using only regular real numbers.

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Commons category: Imaginary numbers

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An imaginary number is the product of a real number and the imaginary unit i, which is defined by its property i = −1. The square of an imaginary number bi is −b. For example, 5i is an imaginary number, and its square is −25. The number zero is considered to be both real and imaginary.

Originally coined in the 17th century by René Descartes as a derogatory term and regarded as fictitious or useless, the concept gained wide acceptance following the work of Leonhard Euler in the 18th century, and Augustin-Louis Cauchy and Carl Friedrich Gauss in the early 19th century.