JEE Main & Advanced Mathematics Functions Question Bank Differentiability

  • question_answer
    Let \[[x]\]denotes the greatest integer less than or equal to x. If \[f(x)=[x\sin \pi x]\], then \[f(x)\]is [IIT 1986]

    A)            Continuous at \[x=0\]

    B)            Continuous in \[(-1,0)\]

    C)            Differentiable in (?1,1)

    D)            All the above

    Correct Answer: D

    Solution :

               Here, when \[-1\le x\le 1,\,\,0\le x\sin \pi x<1\]            \[\Rightarrow \,\,f(x)=[x\,\sin \pi x]=0\]for \[-1\le x\le 1,\,\]            i.e., \[f(x)\] is constant function (equal to zero) in \[[-1,\,\,1].\]            \[\Rightarrow \,\,f(x)\] is differentiable in \[(-1,\,\,1)\].


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