Sunday, 9 March 2014

real analysis - Non-existence of bijective, continuous function from (0,1) to [0,1]





The problem : Give example of a continuous, onto function from (0,1) to [0,1]. Is it possible for such a function to be one-one?



My partial solution : For the 1st part of the question, I came up with this example -



f:(0,1)[0,1] given by f(x)=sin(2πx)



This is continuous and onto, but not one-one.



What I'm asking : For the 2nd part of the question, I feel that it should be provable that there cannot exist a continuous, onto, one-one function from (0,1) to [0,1] (If not, we need a counter-example). Any help regarding this proof (or what would really surprise me, a counter example)?




Thanks in advance.


Answer



Suppose f is bijective, then f must be strictly increasing or decreasing function. W.l.g. take f to be increasing. Then x(0,1) such that f(x)=1. Now take $x1$, which leads to contradiction.


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