Mapping,having difficulty understanding the proof

Question

amistre64 · Answer

Canada is north ... :)

anonymous · Answer

What do you mean ?should I translate them into English

amistre64 · Answer

you should ask a question that can be answered, or responded to that doesnt involve mind reading ....

anonymous · Answer

I don't understand the blue lines part proof,why there is a "so" ,especially,why x belong to A can lead to f(x)belong to f(A)

amistre64 · Answer

you do realize that we cant see what it is that you are looking at and that you need to actually provide us with that context.

amistre64 · Answer

in general, if x is an element of A,  and f maps the elements of A to an image of A, f[A];  then f maps x to f(x) if x is in the usable domain of A

anonymous · Answer

Really ? You can't? I added a attachment,a picture?

anonymous · Answer

I don't really understand ""the image of A"you talked about ,they are sets,I think it is quite natural if x is an element of set A,then f(x) belongs to f(A)

amistre64 · Answer

no files are showing up as attached on my end.

amistre64 · Answer

and just becuase x is in A, does not mean that it is in the domain of the function.

amistre64 · Answer

take the function sqrt(x)  if A is the set of real numbers, then the set of negative real numbers is not in the domain of sqrt(x)

amistre64 · Answer

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