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anonymous

  • one year ago

Help please??? Find S7 for 3 + 8 + 13 + 18 +… 116 121 126 131 Thanks so much <3

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  1. anonymous
    • one year ago
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    Are you asking for the 7th term?

  2. anonymous
    • one year ago
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    yes, the 7 is supposed to be a subscript not just next to it.

  3. anonymous
    • one year ago
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    To find a certain term in the sequence you can use the following \[S_n = \frac{ n }{ 2 }(a+t_n)\] where a is the first term, t_n is the following from sequences \[t_n = a+(n-1) \times d\] where here a = first term, n is the term we are looking for and d = common difference.

  4. anonymous
    • one year ago
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    Sorry that should say term in the "series" not sequence

  5. anonymous
    • one year ago
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    so the equation would be \[t _{n}=3+(n-1)\times5\] ??

  6. anonymous
    • one year ago
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    Looks good, n is the term we are looking for :)

  7. anonymous
    • one year ago
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    What am I supposed to do next? I tried working out the problem but I got 33 and that's not an option

  8. anonymous
    • one year ago
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    33 is good! But note that we have to plug it into the first formula, at the moment you just found term 7 but not S7 \[t_7 = 33\]\[S_n = \frac{ n }{ 2 }(a+t_n)\] notice we plug in t_7 where it's t_n there are it's t_7 :)

  9. anonymous
    • one year ago
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    okay so the equation 7/2(3+33)?

  10. anonymous
    • one year ago
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    Looks good

  11. anonymous
    • one year ago
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    okay I got C. 126

  12. anonymous
    • one year ago
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    sounds good! :)

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spraguer (Moderator)
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