J & K CET Engineering J and K - CET Engineering Solved Paper-2011

  • question_answer
    If \[x\ne 0\] and \[y={{\log }_{e}}\,|2x|,\]  then \[\frac{dy}{dx}\] is equal to

    A)  \[\frac{1}{x}\]

    B)  \[-\frac{1}{x}\]

    C)  \[\pm \,\frac{1}{2x}\]

    D)  None of these

    Correct Answer: A

    Solution :

    If \[x\ne 0,\,\,y\,\,{{\log }_{e}}\,|2x|\] \[y=\left\{ \begin{matrix}    {{\log }_{e}}(-2x), & if\,x<0  \\    {{\log }_{e}}\,(2x), & if\,x>0  \\ \end{matrix} \right.\] \[\frac{dy}{dx}=y'=\left\{ \begin{matrix}    \frac{1}{(-2x)}(-2), & if\,x<0  \\    \frac{1}{(2x)}\,(2), & if\,x>0  \\ \end{matrix} \right.\] \[=\left\{ \begin{matrix}    1/x, & if\,x<0  \\    1/x, & if\,x>0  \\ \end{matrix} \right.\] \[\Rightarrow \] \[\frac{dy}{dx}=\frac{1}{x},\,\,\,if\,\,x\ne 0\]


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