Imaginary Numbers (I)

Imaginary numbers is the set of numbers that are multiples of i (not 1) and whoose square root is -1.

1. $i = \sqrt{i^2} = -1$
2. $b \in R$ (b in all real numbers R)
3. $i \in I$ (i in all imaginary numbers I)
4. $I \ {i} = bi$