JEE Main & Advanced Sample Paper JEE Main - Mock Test - 8

  • question_answer
    The number of values of a for the which the function \[f(x)=(x+1)|x-a|\]is differentiable \[\forall x\in R\], is

    A) 0

    B) 1

    C) 2                     

    D) more than 2

    Correct Answer: B

    Solution :

    [b]: Let function is differentiable in R, then it will be differentiable at x = a. [\[\because \]Possible point of non-differentiability is x = a] \[f'({{a}^{+}})=\underset{h\to {{0}^{+}}}{\mathop{\lim }}\,\frac{(a+h+1)|h|-0}{h}=a+1\] \[{f}'({{a}^{-}})=\underset{h\to {{0}^{+}}}{\mathop{\lim }}\,\frac{(a-h+1)|-h|}{-h}=-\ (a+1)\] Now,\[f'({{a}^{+}})=f'({{a}^{-}})\Rightarrow a=-1\]


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