Let $f (x) =$ $\left[ {\begin{array}{*{20}{c}} {\tfrac{{1\,\, + \,\,\cos \,\,2\,\pi \,x}}{{1\,\, - \,\,\sin \,\,\pi \,x}}\,\,\,\,\,\,\,\,\,\,\,\,\,}&{,\,\,\,\,\,x\,\, < \,\,\tfrac{1}{2}} \\ {p\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,}&{,\,\,\,\,\,x\,\, = \,\,\tfrac{1}{2}} \\ {\tfrac{{\sqrt {2\,x\,\, - \,\,1} }}{{\sqrt {4\,\, + \,\,\sqrt {2\,x\,\, - \,\,1} } \,\,\, - \,\,\,2}}}&{,\,\,\,\,\,x\,\, > \,\,\tfrac{1}{2}} \end{array}} \right.$ . If $f (x)$ is discontinuous at $x =\frac{1}{2}$ , then
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