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Oh I got It, but as I see I can't have something like the image below. For something like the image should I realize another quadrilateral liked to the other one or is the a faster solution?
Sorry, you are totaly right. I don't know but I really forget it. So, I get this: Block[ {a = 0.05, T = 90, x1 = 0, y1 = 20, z1 = 40, x2 = 10, y2 = 10, z2 = 0}, ParametricPlot3D[ {x[t], y[t], z[t]}, {t, 0, T}, ...
Update. I tried to quit the Kernel, but the situation is the same. I'm using Mathematica 11.2 if it helps. Maybe I'm doing something wrong running the code. I do " Evalutate Notebook" to see the output and I still get the same error. But it's...