JEE Main & Advanced Mathematics Functions Question Bank Continuity

  • question_answer
    The value of f at \[x=0\] so that the function \[f(x)=\frac{{{2}^{x}}-{{2}^{-x}}}{x},x\ne 0\], is continuous at \[x=0\], is [Kerala (Engg.) 2005]

    A)            0

    B)            log 2

    C)            4

    D)            \[{{e}^{4}}\]

    E)            log 4

    Correct Answer: E

    Solution :

               \[f(0)=\underset{x\to 0}{\mathop{\lim }}\,f(x)=\underset{x\to 0}{\mathop{\lim }}\,\left( \frac{{{2}^{x}}-{{2}^{-x}}}{x} \right)=\underset{x\to 0}{\mathop{\lim }}\,\left[ \frac{({{2}^{x}}+{{2}^{-x}}){{\log }_{e}}2}{1} \right]\]                    \[=({{2}^{0}}+{{2}^{0}}){{\log }_{e}}2\]                    \[=(1+1){{\log }_{e}}2\]                    \[=2{{\log }_{e}}2={{\log }_{e}}4\].


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