Taz:
Off the top of my head, I don't know what 5634.23 X 123456 is. You come waltzing along and tell me it's -24351. Now, I know for sure that's not right.
Just because we can't tell what's right doesn't mean we can't tell what's wrong.
I wonder if the disagreement on this point isn't illusory.
Speaking precisely, Taz, you
do know what is right. That is why you can see the proposed answer won't work. You know that the right answer, whatever it is, will not be a negative number.
There are limits to what anyone knows, of course. But the proposed answer in your example does not fall outside those limits for you. It contradicts something you really do know.
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Edited by Archer Opterix, : clarity.