What is infinity minus one minus infinity?

It is undefined. The question is written as if the poster thinks of infinity as a number—it is not. The answer is not −1, even though one has an entity minus what appears to be the same entity—sorry, that it does not work that way. read more

Woops! It is impossible for infinity subtracted from infinity to be equal to one and zero. Using this type of math, we can get infinity minus infinity to equal any real number. Therefore, infinity subtracted from infinity is undefined. read more

Infinity minus infinity is a bit iffy, because some infinite functions increase faster or slower than others, so the answer could be infinity, negative infinity, indeterminate, or 0 depending on the question content. read more

or maybe: B is the set of numbers greater than 7; A\B = {1,2,3,4,5,6,7}, so infinity minus infinity is seven (or whatever other number you fancy) or: B is the set of even numbers; A\B is the set of odd numbers, so infinity minus infinity is infinity. read more