Thanks guys...... Here is what I got out of your posts:

To find wheather, x-y=0 or x+y=0 (Yes or No question)

Statement I is self-exlanatory, considering statement II,

The values (x,y) => (0,-6) and (5,-1) is not much useful to prove otherwise.

The values (3,-3) and say (9,3) will be useful.

Both the above x and y values meet the condition of x-y=6, but only (3,-3) meets the condition x+y=0 whereas (9,3) does not. Hence we get Yes and No.

There for insufficent.

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