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    Me amd a frind have spent an hour on this as question and im about to gube up because we hsve gotten NOWHERE please can someone explain 2(ii) Name:  received_1008883735863805.jpeg
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    (Original post by Saffronwillow)
    Me amd a frind have spent an hour on this as question and im about to gube up because we hsve gotten NOWHERE please can someone explain 2(ii) Name:  received_1008883735863805.jpeg
Views: 119
Size:  46.8 KB
    Note that what you have is an arithmetic sequence with common difference -3 and first term 102.

    Now you know the formula for the sum of the first n terms of an arithmetic sequence, don't you?
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    (Original post by Zacken)
    Note that what you have is an arithmetic sequence with common difference -3 and first term 102.

    Now you know the formula for the sum of the first n terms of an arithmetic sequence, don't you?
    Yeah its 102+99+96=297
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    (Original post by Saffronwillow)
    Yeah its 102+99+96=297
    Huh? The sum to n terms is given by \frac{n}{2}(2a + (n-1)d). Just plug in a = 102 and d=-3.

    For the value for which the sum if zero, just set the equation to 0 and solve for n, ignoring non-positive solutions.
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    (Original post by Zacken)
    Huh? The sum to n terms is given by \frac{n}{2}(2a + (n-1)d). Just plug in a = 102 and d=-3.

    For the value for which the sum if zero, just set the equation to 0 and solve for n, ignoring non-positive solutions.
    Oooh, THANK YOU
 
 
 
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