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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

Are you asking for the 7th term?

2. anonymous

yes, the 7 is supposed to be a subscript not just next to it.

3. anonymous

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

Sorry that should say term in the "series" not sequence

5. anonymous

so the equation would be $t _{n}=3+(n-1)\times5$ ??

6. anonymous

Looks good, n is the term we are looking for :)

7. anonymous

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

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

okay so the equation 7/2(3+33)?

10. anonymous

Looks good

11. anonymous

okay I got C. 126

12. anonymous

sounds good! :)

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