Imaginary number
Imaginary numbers are numbers that are made from combining a real number with the imaginary unit, called i, where i is defined as . They are defined separately from the negative real numbers in that they are a square root of a negative real number (instead of a positive real number). This is not possible with real numbers, as there is no real number that will multiply by itself to get a negative number (e.g.,  and ). The set of imaginary numbers are sometimes denoted by the letter .