JEE Main & Advanced Mathematics Functions Question Bank Continuity

  • question_answer
    Let \[f(x)=\,\left\{ \begin{matrix}    \frac{\sin \pi x}{5x}, & x\ne 0  \\    k, & x=0  \\ \end{matrix} \right.\]. If \[f(x)\] is continuous at \[x=0,\] then \[k=\]  [Karnataka CET 2002]

    A)            \[\frac{\pi }{5}\]

    B)            \[\frac{5}{\pi }\]

    C)            1

    D)            0

    Correct Answer: A

    Solution :

               Since \[f(x)\] is continuous at \[x=0,\] therefore \[\underset{x\to 0}{\mathop{\text{lim}}}\,f(x)=f(0)\] Þ \[\underset{x\to 0}{\mathop{\text{lim}}}\,\frac{\sin \pi \,x}{5x}=k\]            Þ \[\underset{x\to 0}{\mathop{\text{lim}}}\,\left( \frac{\sin \pi \,x}{\pi x} \right)\,.\,\frac{\pi }{5}=k\] Þ \[(1)\,.\,\frac{\pi }{5}=k\] Þ \[k=\frac{\pi }{5}\].


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