JEE Main & Advanced Mathematics Functions Question Bank Limits

  • question_answer
    \[\underset{x\to 0}{\mathop{\lim }}\,\frac{{{e}^{\alpha \ x}}-{{e}^{\beta \ x}}}{x}=\]     [MP PET 1994; DCE 2005]

    A)                 \[\alpha +\beta \]

    B)                 \[\frac{1}{\alpha }+\beta \]

    C)                 \[{{\alpha }^{2}}-{{\beta }^{2}}\]

    D)                 \[\alpha -\beta \]

    Correct Answer: D

    Solution :

                       \[\underset{x\to 0}{\mathop{\lim }}\,\,\frac{{{e}^{\alpha x}}-{{e}^{\beta x}}}{x}=\underset{x\to 0}{\mathop{\lim }}\,\,\frac{{{e}^{\alpha x}}-1-{{e}^{\beta x}}+1}{x}\]                     \[=\alpha \underset{x\to 0}{\mathop{\lim }}\,\,\frac{{{e}^{\alpha x}}-1}{\alpha x}-\beta \underset{x\to 0}{\mathop{\lim }}\,\,\frac{{{e}^{\beta x}}-1}{\beta x}\]\[=\alpha .1-\beta .1=\alpha -\beta .\]


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