\textbf{115-} The function with the rule $f(x) = \begin{cases} \dfrac{x-[x]}{x^2-x-6} & ; \ x \neq 2 \\ a & ; \ x = 2 \end{cases}$, for which value of $a$, is continuous on the interval $[2,3]$?
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(1) $\dfrac{1}{11}$ \hfill (2) $\dfrac{1}{9}$ \hfill (3) $\dfrac{1}{8}$ \hfill (4) $\dfrac{1}{6}$
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