What is the x coordinate or y coordinate of a point is 0?

If you mean at the Origin (where both X and Y cross), then the coordinates would be (0,0)

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-- If the 'x' coordinate is zero, then the point is on t he y-axis.

-- If the 'y' coordinate is zero, then the point is on the x-axis.

-- If both coordinates are zero, then the point must be the one
that's on both axes ... the 'origin'.