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half or quarter of cylinder

circle

The parametric equation of a circle with radius r is: x = r . cos y = r . sin with from 0 to 360°

cylinder

If we add a linear parameter h for z we can define a cylinder: x = r . cos y = r . sin z = h with from 0 to 360° and h from 0 to the height of the cylinder. Shuffling the three expressions we can make the cylinder standing up or lying down. Changing the Start and/or End Value of the angle, we can create e.g. a half or a quarter of a cylinder. The GeoGebra command to draw such parametric surfaces is: Surface( , , , , , , , , )