Is a line lying in a plane an open or a closed region?

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Question from pardeep, a student:

please help with this question on the open and closed intervals ::
Is a line lying in a plane an open or a closed region? my teacher says it is a closed region reasoning out that it contains all it boundary points . please help how is it so?

Hi,

Your teacher is correct, a line in the plane is a closed subset of the plane. I would have said that it is closed since it contains all its limit points.

Harley

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