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Math Help - find value

  1. #1
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    find value

    Hello friends ,
    I trying to solve some question papers where i came across this question

    if (1^2+2^2+3^2....+10^2)=385 then the value of (2^2+4^2+6^2....+20^2) is:

    can anbody tell how to solve this equation ............

    in shortcut way .......

    thanku.................
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  2. #2
    MHF Contributor
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    Re: find value

    Hey manishamishra.

    In the first question you are adding up n^2 terms and in the second one you are adding up (2n)^2 terms in a summation.

    You can factorize out the (2n)^2 to give 4n^2 which means you have 4 * Summation of n^2 and since you have the summation for n^2 you can get the summation for (2n)^2.
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