Wednesday, 20 May 2015

Negative solution for a positive continued fraction



x=1+11+11+...x=1+1xx=1±52
Can the negative solution be considered as a solution? If yes, how is it possible to have a negative solution for a positive continued fraction? If no, how do we prove that it can't be a solution?



Edit 1: I want to understand the assumption we are considering while forming the equation which results in the "extraneous solution".


Answer



No, the negative number is not a solution. You showed that if x is equal to that fraction, then it is either 1+52 or 152. You calculated possible candidates for solutions, not the solution itself.




You can prove that x must be positive by simply arguing that x is a limit of a sequence with only positive elements, so the limit (if it exists, which should also be proven) must be positive.


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