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## Homework Statement

Show that the subset D={(x,y)| x≠0 and y≠0} is an open set in R^2

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## Homework Equations

Open set: U is a subset of R^n. U is an open set when for every point X1, contained within U, there exists some open disk centered around X1 with radius r>0, that is completely contained within U. Or for simplicity's sake, a set U is open if it does not contain any of its boundary points.

## The Attempt at a Solution

I have an understanding of what makes up an open set and know why this set is open, but i have no idea as to how I am meant to prove this, graphically or analytically( ideal method).

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