Question

What does this fancy X symbol stand for?

Answer 1

you know what the fancy R is, right?

Answer 2

the fancy X is some set of numbers which is mapped by f into the reals. not sure specifically what set the fancy X represents... but it is some set. I'll hunt around and see if I can find out

Answer 3

if your course material hasnt defined it, then it should be a generic set i believe

Answer 4

the fancy X just denotes the domain. the problem should specify or it could be somehow implied just exactly what the set is.

Answer 5

this is what it says:

Answer 6

X is a subset of the real line R

Answer 7

yeah but the fancy X looks different

Answer 8

I suppose it makes sense...but they shouldn't have done that, confusing students should be a criminal offence.

Answer 9

though if I am not mistaken, putting that fancy X in there would have taken some effort...
could have been deliberate...

Answer 10

In your definition g(x) is a positive function, so I think that definition is specialized to positive functions.
Generally, when a mathematician want to state something about a real functions, he indicates its domain as generic subset X of the real line

Answer 11

Sometimes the mathematicians use the X to indicate a generic metric space or even a generic vector space

Answer 12

other usage is:
X = Banach space
X = Hilbert space

Answer 13

well, its obviously not any of those

Answer 14

oops.. in your definition g(x) is not a positive function, I'm sorry I have made an error

Answer 15

sure, but please keep in mind that a subset of a real function can be viewed as a metric space itself, and it viewed even as a topological space

Answer 16

in my textbook of topology, X is used in order to indicate a topological space

Answer 17

ok...but I still think they shouldn't have done it