On a Cartesian Plane where is the unit usually represented as i or j?

Question

What is the official nickname of a particularly large capacity plane, built by Airbus and used to transport large dimension loads, from pieces of art to space station parts and whole helicopters?

Answer 1

Vertical axis
The unit is the imaginary number which is the square root of -1, and the numbers and the Cartesian plane in which it is used are termed complex. In the complex Cartesian plane imaginary numbers, e.g. i or j, lie on the vertical axis. The complex plane is sometimes called the Argand plane or Gauss plane.