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JEE Main & Advanced Mathematics Binomial Theorem and Mathematical Induction Question Bank Critical Thinking

  • question_answer
    If the coefficient of \[{{(2r+4)}^{th}}\] and \[{{(r-2)}^{th}}\]terms in the expansion of \[{{(1+x)}^{18}}\]are equal, then r= [MP PET 1997; Pb. CET 2001]

    A) 12

    B) 10

    C) 8

    D) 6

    Correct Answer: D

    Solution :

    \[^{18}{{C}_{2r+3}}{{=}^{18}}{{C}_{r-3}}\,\,\,\Rightarrow 2r+3+r-3=18\Rightarrow r=6\]


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