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JEE Main & Advanced Mathematics Sequence & Series Question Bank Geometric Progression

  • question_answer
    The \[{{20}^{th}}\] term of the series \[2\times 4+4\times 6+6\times 8+.......\]will be [Pb. CET 1988]

    A) 1600

    B) 1680

    C) 420

    D) 840

    Correct Answer: B

    Solution :

    The given series \[2\times 4+4\times 6+6\times 8....\]\[{{n}^{th}}\] terms \[{{T}_{n}}=2n\ .\ 2(n+1)=4n(n+1)\] Putting\[n=20\], we get\[{{T}_{20}}=4\ .\ 20(20+1)=1680\].


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