# Thread: The mystery with infinity

1. Here is a question
what is
[-infinity][infinity] = ?

Is it not determined or [+infinity] or [-infinity] or simply 0 ?

2.

3. The answer is indeterminate. It really has no meaning.

4.

5. In real arithmetic, infinity is not a number but a limit, so it would depend on how you reached that infinity (though it'll usually be negative). But it will never be zero because the only way for a * b to be 0 is if a or b is zero.

6.

7. The real projective line can be thought of as a line whose endpoints meet at infinity.

Real projective line - Wikipedia, the free encyclopedia

8. When people ask about arithmatic the standard response would be to look at the extended reals and follow the rules there. In this case, .

Wiki is your friend here: Extended real number line - Wikipedia, the free encyclopedia

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