## anonymous 3 years ago Write each arithmetic series as the sum of terms, find each sum.

1. anonymous

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2. anonymous

it similar by : 3(1) + 3(2) + 3(3) + 3(4) + ... + 3(10) = 3(1+2+3+4+...+10) = ......

4. anonymous

so im wrong, i thought you were supposed to use the formula, Sn=n(a1+an)/2

5. anonymous

That wording is a bit interesting. Are there multiple questions like this to find the answer for, or just this one?

6. anonymous

yea there are about 8 questions that are under that two part question

7. anonymous

Your formula would work; you must have done it wrong.

8. anonymous

$S_{n} = \frac{n}{2} (a_{1} + a_{n})$ Did you use 10 for $$n$$ and 3 for $$a_{1}$$?

for : n=1 ----> 3(1) = 3 n=2 ----> 3(2) = 6 n=3 ----> 3(3) = 9 .... so on, the series be 3+6+9+....+30 yes, use the formula like @geoffb said :)

10. anonymous

for n, i put 10, a1, i put 1, and for A n, i put 3

11. anonymous

Okay, that's the problem. $$a_{1}$$ means the value of your first term (which is 3 times 1, or 3). $$a_{n}$$ means the value of your n-th term. In this case, n is 10, so the value of the 10th term is 3 times 10, or 30.

12. anonymous

i got 75, am i right?

13. anonymous

14. anonymous

|dw:1354172733466:dw|

15. anonymous

Why are you using 10 for $$a_{n}$$?

16. anonymous

It wants $$a_{n}$$, not $$n$$.

17. anonymous

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18. anonymous

That looks great.

19. anonymous

ughhh finally!

20. anonymous

so i get 330/2=165

21. anonymous

Yup. :)