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1. I have a question determine the sum of the first 50 terms in the series:

1 + 1/3 + 1/3^2 + 1/3^3 + ...

Now im led to believe that I will be using the formula:

S(n) = n/2 (2a(1) + (n-1) d)

But I cant seem to find the 'd' in this formula as in the classroom all the examples we did the differences in each sequence were always the same

any help?
2. (Original post by picklesmartyn)
I have a question determine the sum of the first 50 terms in the series:

1 + 1/3 + 1/3^2 + 1/3^3 + ...

Now im led to believe that I will be using the formula:

S(n) = n/2 (2a(1) + (n-1) d)

But I cant seem to find the 'd' in this formula as in the classroom all the examples we did the differences in each sequence were always the same

any help?
You are mistaken. This is a GEOMETRIC series not an arithmetic series.
3. oh right so il need

S(n) = a(1) (r(n) - 1) / r - 1

and in this case will struggle to find 'r'
4. (Original post by picklesmartyn)
oh right so il need

S(n) = a(1) (r(n) - 1) / r - 1

and in this case will struggle to find 'r'
Really?

1/3 divided by 1 = ?
5. wow that was very bad from me

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