Definition:Complex Number/Imaginary Unit

Definition
Let $\C = \left\{{a + b i: a, b \in \R}\right\}$ be the set of complex numbers.

The entity $i := 0 + 1 i$ is known as the imaginary unit.

Also denoted as
Using the formal definition of complex numbers it is the ordered pair $\left({0, 1}\right)$.

The non-italicized $\mathrm i$ can also be seen.