BCECE Engineering BCECE Engineering Solved Paper-2008

  • question_answer
    \[\underset{x\to \infty }{\mathop{\lim }}\,[{{x}^{2}}+2x-1]\]is equal to

    A) \[\infty \]                              

    B)         \[\frac{1}{2}\]                     

    C)  4                            

    D)         1

    Correct Answer: D

    Solution :

    \[\underset{x\to \infty }{\mathop{\lim }}\,[\sqrt{{{x}^{2}}+2x-1}-x]\] \[=\underset{x\to \infty }{\mathop{\lim }}\,\left[ \frac{(\sqrt{{{x}^{2}}+2x-1}-x)(\sqrt{{{x}^{2}}+2x-1}+x)}{\sqrt{{{x}^{2}}+2x-1}+x} \right]\] \[=\underset{x\to \infty }{\mathop{\lim }}\,\left[ \frac{{{x}^{2}}+2x-1-{{x}^{2}}}{\sqrt{{{x}^{2}}+2x-1}+x} \right]\] \[=\underset{x\to \infty }{\mathop{\lim }}\,\left[ \frac{2-\frac{1}{x}}{\sqrt{1+\frac{2}{x}-\frac{1}{{{x}^{2}}}+1}} \right]\] \[=\frac{2}{2}=1\]


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