Saturday, 10 January 2015

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



Determine whether the function $y=\tan x$ is uniformly continuous in the open interval $(0,\pi/2)$.



I tried approaching it this way




Let $x,y \in (0, \pi/2)$. Then



$$|f(x)-f(y)|=|\tan x-\tan y|={\left|{{\sin x\cos y-\cos x\sin y}\over \cos x\cos y}\right|}\le|\sin(x-y)|\le|x-y|$$



Selecting $\delta=\epsilon$ 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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