Thursday, 18 June 2015

elementary set theory - Proof about cardinality of sets |RZ|=|R|




Prove that |RZ|=|R| where R is reals and Z is integers.




New approach
Maybe the problem is reduced to finding a bijection between (0,1) and [0,1] if we find a bijection between these intervals, we can do the same thing for the other ones



What about this possible bijective function f(x)=1/(x-1)x




Thank you so much for your help, I have more problems like this to work on, so need more help.


Answer



Assume it is known that any open, nonempty subset of R is uncountable - this step is where your work may be. The rest is easy:



Let S=RZ.



First remark that SR, so we must have that |S||R|.



The open interval (0,1) is a subset of SR, so |(0,1)||S||R|.




But |R|=|(0,1)|, and we're done.



NOTE: to see that |R|=|(0,1)|, we might construct a bijection f:(0,1)(0,) such that f(x)=11x1, and reason that this bijection can be easily extended to a bijection between (0,1) and R.


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