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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
    If the coefficients of  \[{{r}^{th}}\]term and \[{{(r+4)}^{th}}\]term are equal in the expansion of \[{{(1+x)}^{20}}\], then the value of r will be [RPET 1985, 97; Kerala (Engg.) 2001; MP PET 2002]

    A) 7

    B) 8

    C) 9

    D) 10

    Correct Answer: C

    Solution :

    \[^{20}{{C}_{r-1}}{{=}^{20}}{{C}_{r+3}}\]\[\Rightarrow \] \[20-r+1=r+3\Rightarrow r=9\].


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