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anonymous

  • one year ago

Help please?? Find S12 for the series 2 + 5 + 8 +...

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  1. anonymous
    • one year ago
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    you do see that it's adding 3 each time so the sequence would be starting from 8 would be. 8, 11, 14, 17, 20, 23, 26, 29, 32. and so on.

  2. anonymous
    • one year ago
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    So its 35?

  3. anonymous
    • one year ago
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    ok what is the whole question? cause I just saw that it's adding each number. whats the whole question?

  4. anonymous
    • one year ago
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    You want to find the sum to the twelfth term. So you use the formula n/2 * (a + L)

  5. anonymous
    • one year ago
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    That is the whole question.

  6. triciaal
    • one year ago
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    this is an arithmetic progression the first term ,a = 2 and the common difference , d = 3 the nth term is a + (n-1)d the sum of the first n terms is given by n/2(2a + (n-1)d) The question has S12 so I think it needs the sum not when n= 12 as above.

  7. anonymous
    • one year ago
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    222

  8. triciaal
    • one year ago
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    @JackJordan can you explain your formula?

  9. anonymous
    • one year ago
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    It's standard a-level formula needs no explaining.

  10. anonymous
    • one year ago
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    So which ones the right answer? I'm kind of confused.

  11. anonymous
    • one year ago
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    How rude of me. Of course it does... you take the sum of an arithmetic series and another, reverse their order. Add then cancel terms. And you will reach the above formula. Can't fit it here but google "sum of arithmetic series"

  12. anonymous
    • one year ago
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    The answer is 222. My calculator malfunctioned earlier on.

  13. anonymous
    • one year ago
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    in all honesty so am I, I never seen this formula before. i'm only in 8th grade

  14. anonymous
    • one year ago
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    I'm in British College (posh?)... the formula is pretty standard. You can add the numbers up yourself if you want to check.

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