Saturday, 10 January 2015

real analysis - Is function y=tanx uniformly continuous in the open interval (0,pi/2);?



Determine whether the function y=tanx is uniformly continuous in the open interval (0,π/2).



I tried approaching it this way




Let x,y(0,π/2). Then



|f(x)f(y)|=|tanxtany|=|sinxcosycosxsinycosxcosy||sin(xy)||xy|



Selecting δ=ϵ we have that the given function is uniformly continuous.



Where am i gong wrong ?


Answer



Every uniformly continuous function is bounded on every bounded interval included in its domain of definition. The proof only uses that the real line is Archimedean.


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