https://en.wikipedia.org/wiki/Imaginary_number

An imaginary number is a complex number that can be written as a real number multiplied by ... At the time imaginary numbers, as well as negative numbers, were poorly understood and regarded by some as fictitious or useless, much as zero ...

https://en.wikipedia.org/wiki/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 a solution of the equation x2 = −1. Because no real number satisfies this equation, i is called an imaginary ... Despite the historical nomenclature "imaginary", complex numbers are regarded in the mathematical ...

http://rossroessler.tripod.com/

Formulas for solving 3rd and 4th degree polynomial equations were discovered, and people realized that some work with square roots of negative numbers ...

https://www.quora.com/Who-discovered-imaginary-numbers

The need for imaginary numbers didn't arrive until significant discoveries were made in algebra, namely the discovery of negative numbers.

http://www.math.uri.edu/~merino/spring06/mth562/ShortHistoryComplexNumbers2006.pdf

notes track the development of complex numbers in history, and give evidence that ... The methods of algebra known to the arabs were introduced in Italy by the Latin transla- .... on the Geometrical Interpretation of Imaginary Quantities”.

https://medium.com/i-math/imaginary-numbers-explained-e5aa63bdb7ae

Jul 26, 2017 ... We were talking about number systems when I mentioned the imaginary numbers and she burst into laughter. “What's so funny?” “Imaginary ...

https://www.sciencefocus.com/science/a-brief-introduction-to-imaginary-numbers/

4 days ago ... Just because imaginary numbers don't exist, it doesn't mean they are ... to ballistics and fortifications expert Niccolo Tartaglia were quadratic ...