I would like to draw figures in 2D…

for example, the parametric equations of a circle…

x=r* cos t

y=r *sin t

you can obtain the Cartesian coordinates which can be given by

x^2+y^2 < r^2

and then for each (x,y) coordinates which obey the last formula you draw a circle in a plain.

With the cone I know…

The circular base has z=0,x2+y2<r2. The curved surface has x2+y2=(r-(rz/h))2, for z in the range [0, h].

x = ((h-u)/h) * r * cos theta

y = ((h-u)/h) * r * sin theta

z = u

where u (0,h) y theta (0,2pi)

The question how can I obtain a formula/s in Cartesian coordinates that allows me to draw it?

It is a good challenge…