CEE Kerala Engineering CEE Kerala Engineering Solved Paper-2007

  • question_answer
    If\[y=\underset{n\to \infty }{\mathop{\lim }}\,(1+x)(1+{{x}^{2}})(1+{{x}^{4}})\]\[...(1+{{x}^{2n}}\text{ })\]and\[{{x}^{2}}<1,\]then y is equal to

    A)  1                                            

    B)   \[\frac{1}{1-x}\]

    C)  \[\frac{1}{1+x}\]             

    D)         \[\frac{-1}{{{(1-x)}^{2}}}\]

    E)  \[\frac{1}{{{(1-x)}^{2}}}\]

    Correct Answer: E

    Solution :

    \[y=\underset{n\to \infty }{\mathop{\lim }}\,(1+x){{(1+x)}^{2}}(1+{{x}^{4}})....(1+{{x}^{{{2}^{n}}}})\] \[=\underset{n\to \infty }{\mathop{\lim }}\,\frac{(1-x)(1+x)(1+{{x}^{2}})(1+{{x}^{4}})....(1+{{x}^{{{2}^{n}}}})}{(1-x)}\] \[=\underset{n\to \infty }{\mathop{\lim }}\,\frac{(1-{{x}^{2}})(1+{{x}^{2}})(1+{{x}^{4}})....(1+{{x}^{{{2}^{n}}}})}{1-x}\] \[\Rightarrow \]               \[y=\underset{n\to \infty }{\mathop{\lim }}\,\frac{1-{{x}^{{{2}^{n+1}}}}}{1-x}=\frac{1}{{{(1-x)}^{2}}}\]           \[\Rightarrow \]               \[y=\frac{1}{{{(1-x)}^{2}}}\]


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