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

  • question_answer
    If the coefficient of the middle term in the expansion of \[{{(1+x)}^{2n+2}}\]is p and the coefficients of middle terms in the expansion of \[{{(1+x)}^{2n+1}}\] are q and r, then

    A) \[p+q=r\]

    B) \[p+r=q\]

    C) \[p=q+r\]

    D) \[p+q+r=0\]

    Correct Answer: C

    Solution :

    Since (n+2)th term is the middle term in the expansion of \[{{(1+x)}^{2n+2}}\],  therefore \[p={{\,}^{2n+2}}{{C}_{n+1}}\]. Since (n+1)th and (n+2)th terms are middle terms in the expansion of (1+x)2n+1, therefore \[q={{\,}^{2n+1}}{{C}_{n}}\] and \[r={{\,}^{2n+1}}{{C}_{n+1}}\] But \[^{2n+1}{{C}_{n}}+{{\,}^{2n+1}}{{C}_{n+1}}={{\,}^{2n+2}}{{C}_{n+1}}\] \[\therefore \,\,\,q+r=p\]


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