The imaginary number 
, i.e., the square root
of 
. The imaginary unit is denoted and
commonly referred to as "i." Although there
are two possible square roots of any number, the square roots of a negative number
cannot be distinguished until one of the two is defined as the imaginary unit, at
which point 
and 
can then be distinguished. Since either choice is possible, there is no ambiguity
in defining 
as "the" square root of 
. In the Wolfram
Language, the imaginary unit is implemented as I.
Imaginary Unit
See also
Complex Number, i, Imaginary Number, UnitRelated Wolfram sites
http://functions.wolfram.com/Constants/I/Explore with Wolfram|Alpha
Cite this as:
Weisstein, Eric W. "Imaginary Unit." From MathWorld--A Wolfram Web Resource. https://mathworld.wolfram.com/ImaginaryUnit.html