JEE Main & Advanced Mathematics Functions Question Bank Differentiability

  • question_answer
    Let \[h(x)=\min \{x,\,{{x}^{2}}\},\]for every real number of x. Then [IIT 1998]

    A)            h is continuous for all x

    B)            h is differentiable for all x        

    C)            \[h'(x)=1\], for all \[b=1\]

    D)            h is not differentiable at two values of x

    Correct Answer: A

    Solution :

     \[x\le {{x}^{2}}\,\Rightarrow \,\,x\,(1-x)\le 0\]\[\Rightarrow \,\,x\,(x-1)\ge 0\]                    \[\Rightarrow \,\,x\le 0\] or \[x\ge 1\];  \[\therefore \,\,\,h(x)=\left[ \begin{array}{*{35}{r}}    x\,\,\,\,: & x\le 0  \\    {{x}^{2}}: & 0<x<1  \\    x\,\,\,\,: & x\ge 1  \\ \end{array} \right.\]            \[h\,\,(x)\] is continuous for every x but not differentiable at \[x=0\] and 1. Also \[{h}'(x)=\left[ \begin{array}{*{35}{r}}    1 & x<0  \\    \text{not exists} & x=0  \\    2x & 0<x<1  \\    \text{not exists} & x=1  \\    1 & x>1  \\ \end{array} \right.\]            \[\therefore \,\,\,\,{h}'(x)=1\]for all\[x>1\].


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