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Which subsets of the real number system are closed under division by a nonzero number?
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The meaning of your request is really UNCLEAR.
It is written in so mathematically illiterate way, that I should spend half an hour (or more) to explain WHY it is so,
and explain HOW it SHOULD BE, which (time) I definitely do not have to spend it for nothing.
When a person comes with such or similar question, he/she should have some preliminary pre-requisites
and formulate his/her question correctly in the frame of these pre-requisites, in mathematically correct form.
Then he/she may expect to get an adequate answer.
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Actually, the field of real numbers has INFINITELY MANY sub-fields.
They are sub-fields
- Q (rational numbers),
- (an extension of Q with irrationality ),
- (an extension of Q with irrationality ),
- (an extension of Q with irrationality ),
. . . and infinitely many other sub-fields of the form , where positive integer number n is not a perfect square, . . .
- (an extension of Q with irrationalities and ),
- (an extension of Q with irrationalities and ),
- (an extension of Q with irrationalities and ),
. . . and infinitely many other sub-fields of the form , where m and n are different non-square positive integer numbers, . . .
- (an extension of Q with irrationality ),
- (an extension of Q with irrationality ),
- (an extension of Q with irrationality ),
. . . and infinitely many other sub-fields of the form , where integer number n is not a perfect cube, . . .
and so on and so on . . . - - - infinitely many others.
Each of these sub-fields is a sub-set of real numbers, closed relative addition, subtraction,
multiplication and division by a non-zero elements of these sub-fields.
By the way, when in the school, you learn about getting rid of irrationality in denominators,
you actually learn that the extension is a field over Q.