Infinity is essentially a never-ending variable. The solution to infinity minus one is infinity. However, what mathy showed was also correct, just for a slightly different problem. What mathy showed was the solution to "infinity - 1 = infinity", where you would be trying to find the variable. Infinity is not a set number, so if you subtract 1, it will still be infinity. However, something to note in mathy's version is that you wouldn't subtract infinity from both sides, you would add 1 to each because you are trying to find a variable, not 1. But it is impossible to add or subtract a set number from an unset number. So you get infinity = infinity.