JEE Main & Advanced Mathematics Binomial Theorem and Mathematical Induction Question Bank General term, Coefficient of any power of x, Independent term, Middle term and Greatest term and Greatest coefficient

  • question_answer
    The interval in which  x must lie so that the greatest term in the expansion of \[{{(1+x)}^{2n}}\]has the greatest coefficient, is

    A) \[\left( \frac{n-1}{n},\frac{n}{n-1} \right)\]

    B) \[\left( \frac{n}{n+1},\frac{n+1}{n} \right)\]

    C) \[\left( \frac{n}{n+2},\frac{n+2}{n} \right)\]

    D) None of these

    Correct Answer: B

    Solution :

    Here the greatest coefficient is \[^{2n}{{C}_{n}}\] \[\therefore \,\,{{\,}^{2n}}{{C}_{n}}{{x}^{n}}{{>}^{2n}}{{C}_{n+1}}{{x}^{n-1}}\Rightarrow x>\frac{n}{n+1}\] and \[^{2n}{{C}_{n}}{{x}^{n}}>{{\,}^{2n}}{{C}_{n-1}}{{x}^{n+1}}\Rightarrow x<\frac{n+1}{n}\] Hence the required interval is \[\left( \frac{n}{n+1},\,\frac{n+1}{n} \right)\].


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