How Can We Map the Open Interval (0,1) to the Real Line R Using a Homeomorphism?

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An explicit homeomorphism from the open interval (0,1) to the real line R can be constructed using the function f(x) = (2x - 1) / (1 - (2x - 1)²), which is a bijection. The discussion also references the known homeomorphism from (-1,1) to R using the tangent function, f(x) = tan(πx/2). Participants express difficulty in modifying trigonometric functions and explore alternative mappings, questioning whether a trig function is necessary. Additionally, there is a request for a metric on (0,1) that maintains the same topology as the standard absolute value metric while rendering the open interval complete. The conversation emphasizes the importance of understanding homeomorphisms and their properties in topology.
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Homework Statement


Find an explicit homeomorphism from (0,1) to R.


Homework Equations


A homeomorphism from (-1,1) to R is f(x)=tan(pi*x/2).


The Attempt at a Solution


I'm horrible a modifying trig functions. Obviously, to shift by b you add b to (x) and you can change the frequency by including a scalar to pi. I tried f(x)=tax(2pi*(x+1)/2), but this doesn't do the trick.
 
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You are close, you just need to change a few things. Also Do you have to use a trig function? What about x/1-x2, that maps (-1,1) -> ℝ, could you modify that?
 
Last edited:
6.28318531 said:
You are close, you just need to change a few things. Also Do you have to use a trig function? What about x/1-x2, that maps (-1,1) -> ℝ, could you modify that?

Consider: ##f: (0,1) → \mathbb{R} \\
\ \ x → \frac{2x-1}{1-(2x-1)^2} ##

This mapping is a Homeomorphism. meaning a Bijection.
could someone specify a metric on (0,1) that defines (the same topology) as the abs. value (i.e. the usual) metric and makes this open interval into a complete set?
 
Question: A clock's minute hand has length 4 and its hour hand has length 3. What is the distance between the tips at the moment when it is increasing most rapidly?(Putnam Exam Question) Answer: Making assumption that both the hands moves at constant angular velocities, the answer is ## \sqrt{7} .## But don't you think this assumption is somewhat doubtful and wrong?

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