That’s not true though. While there isn’t a standard, convention is to have z up in mathematics, as z is extending the xy plane we normally work with into a third space.

On paper, when I was learning Descartes’ coordibate system, we used Y as up and X as left-right. And when it was time to plot in 3D, we used Z to “extend” the plane into yourself and away from yourself.

You just hold your sheet of paper perpendicular to the ground (or just use a whiteboard) and it all makes sense.

That’s not true though. While there isn’t a standard, convention is to have z up in mathematics, as z is extending the xy plane we normally work with into a third space.

Might depend on where you were learning.

On paper, when I was learning Descartes’ coordibate system, we used Y as up and X as left-right. And when it was time to plot in 3D, we used Z to “extend” the plane into yourself and away from yourself.

You just hold your sheet of paper perpendicular to the ground (or just use a whiteboard) and it all makes sense.