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Hopefully it's a question.

In 2D geometry the graph of an equation involving x and y is a curve in the plane. In three-dimensional geometry an equation in x, y, and z represents a surface in space.

I couldn't understand about the Surface, here's a picture I modified through ms. paint:

enter image description here

There's a thing that is even confusing me :

enter image description here

Is this a plane ? The thing is its width is over increasing along the y-axis while it should be y=0 Then what would I call it in my B-picture above?

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    A plane is a surface whose points are aligned according to two directions. – 2017-01-14
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    Well now that's confusing me even more :D, btw if point *(x,y,z)* should be on the surface, then picture C is the surface right? or is it, picture C is a plane and surface as well? – 2017-01-14
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    Any connected bidimensional subdomain is a surface. But a plane has the same normal for each of its points. I can't tell from your picture if C is a plane, for sure it seems a surface. Figure 5 is a plane (both x and y are not limited for a plane). – 2017-01-14

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