Manipal Engineering Manipal Engineering Solved Paper-2012

  • question_answer
    The function\[f(x)=\frac{\ln (1+ax)-\ln (1-bx)}{x}\]is not defined at\[x=0\]. The value which should be assigned to\[f\]at\[x=0\]so that it is continuous at\[x=0\],is

    A) \[a-b\]                 

    B) \[a+b\]

    C) \[a-b\]                 

    D)  None of these

    Correct Answer: B

    Solution :

    For\[f(x)\]to be continuous, we must have                 \[f(0)=\underset{x\to 0}{\mathop{\lim }}\,f(x)\] \[\therefore \]  \[\underset{x\to 0}{\mathop{\lim }}\,\frac{\log (1+ax)-\log (1-bx)}{x}\]                 \[=\underset{x\to 0}{\mathop{\lim }}\,\,\frac{a\log (1+ax)}{ax}+\frac{b\log (1-bx)}{-bx}\] \[=a.1+b.1\,\left[ \text{using}\,\underset{x\to 0}{\mathop{\lim }}\,\,\frac{\log (1+x)}{x}=1 \right]\] \[=a+b\] \[\therefore \,f(0)\,=a+b\]


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