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## Main Question or Discussion Point

Hi,

I have a question about identifying closed and open surfaces.

Usually, when I see some exercises in the subject of the divergence theorem/flux integrals, I am not sure when the surface is open and needed to be closed or if it is already closed.

I mean for example a cylinder that is truncated, or tetrahedron in the first octant(x,y,z>=0)... I have seen some exercises that also add the "cover" to close the surface and some that don't.

How should I figure out what to do in a given exercise to help me understand when I should closed the surface or not.

Thank you!

I have a question about identifying closed and open surfaces.

Usually, when I see some exercises in the subject of the divergence theorem/flux integrals, I am not sure when the surface is open and needed to be closed or if it is already closed.

I mean for example a cylinder that is truncated, or tetrahedron in the first octant(x,y,z>=0)... I have seen some exercises that also add the "cover" to close the surface and some that don't.

How should I figure out what to do in a given exercise to help me understand when I should closed the surface or not.

Thank you!