Let $f(x)=\{\begin{array}{cc}\frac{1}{4}sec(\frac{}{2}x),& x<mn>1</mn><mn>1</mn>\\ ,& x=11.\text{E}\text{v}\text{a}\text{l}\text{u}\text{a}\text{t}\text{e}\text{t}\text{h}\text{e}\text{f}\text{o}\text{l}\text{l}\text{o}\text{w}\text{i}\text{n}\text{g}\text{:}& \\ \frac{-4}{x-11},& x>11\end{array}$

$f(11)=$

$\underset{x{11}^{-}}{lim}f(x)=$

$\underset{x{11}^{+}}{lim}f(x)=$

$\underset{x11}{lim}f(x)=$

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