JEE Main & Advanced Mathematics Functions Question Bank Differentiability

  • question_answer
                                                                            \[f(x)=\left| \left| x \right|-1 \right|\] is not differentiable at [IIT Screening 2005]

    A)            0

    B)                                                                                              \[\pm 1,\,0\]

    C)            1

    D)                                                                                                \[\pm \,1\]

    Correct Answer: B

    Solution :

                                                                                         \[=\left\{ \begin{align}   & |x|-1,\,\,\,\,\,\,\,|x|-1\ge 0 \\  & -|x|+1,\,\,\,|x|-1<0 \\ \end{align} \right.\]                                                                                                                                                                           \[=\left\{ \begin{align}   & |x|-1,\,\,\,x\le -1\,\,\text{or}\,x\ge 1 \\  & -|x|+1,\,\,\,\,\,\,\,-1<x<1 \\ \end{align} \right.\]                                                                                                                                                                           \[=\left\{ \begin{align}   & -x-1,\,\,\,\,\,x\le -1 \\  & x+1,\,\,\,\,\,\,-1<x<0 \\  & -x+1,\,\,\,\,\,0\le x<1 \\  & \,\,x-1,\,\,\,\,\,\,\,x\ge 1 \\ \end{align} \right.\]                  From the graph. It is clear that                                                                                                   \[f(x)\]  is not differentiable at                                                                                                \[x=-1,\,0\]  and 1.


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