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When the first n positive integers are added together, their sum is given by
1/2n(n+1)

Find the value of n for which the sum is 105..

Can you show me a step by step please?

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  1. set 1/2n(n+1) = 105
    multiply by 2
    n(n+1) = 210
    n^2 + n - 210 = 0
    (n+15)(n-14) = 0
    n = -15 or 14, but n has to be a positive integer, so

    there are 14 terms

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  2. Thankyou

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