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JEE Main & Advanced Sample Paper JEE Main Sample Paper-28

  • question_answer
    If for positive integers \[r>1,\,\,n>2\], the coefficients of the \[{{(3r)}^{th}}\] and \[{{(r+2)}^{th}}\] power of \[x\] in the expansion of \[{{(1+x)}^{2n}}\] are equal, then n is equal to

    A)  \[2r-1\]                               

    B)  \[2r+1\]

    C)  \[3r\]                   

    D)  \[r+1\]

    Correct Answer: B

    Solution :

    \[^{2n}{{C}_{3r}}{{=}^{2n}}{{C}_{r+2}}\Rightarrow 4r+2=2n\Rightarrow n=2r+1\]


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