JEE Main & Advanced Mathematics Functions Question Bank Differentiability

  • question_answer
    If \[f(x)=\left\{ \begin{align}   & \,\,\,\,\,\,\,\,\,\,\,\,1,\,\,x<0 \\  & 1+\sin x,\,\,0\le x<\frac{\pi }{2} \\ \end{align} \right.\]then \[f'(0)=\] [MP PET 1994]

    A)            1

    B)            0

    C)            \[\infty \]

    D)            Does not exist

    Correct Answer: D

    Solution :

               \[Rf'(0)=\underset{h\to 0}{\mathop{\lim }}\,\frac{f(0+h)-f(0)}{h}=\underset{h\to 0}{\mathop{\lim }}\,\frac{1+\sinh -1}{h}=1\]                    \[f'(0)=\underset{h\to 0}{\mathop{\lim }}\,\frac{f(0-h)-f(0)}{-h}=\underset{h\to 0}{\mathop{\lim }}\,\frac{1-1}{-h}=0\]                    Hence, \[f'(0)\] does not exist.


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