SOLUTION: Calculate 12 + 19 + 26 + ... + (7n+5), if n=1, 2, 3, ..., 10

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Question 1134648: Calculate 12 + 19 + 26 + ... + (7n+5), if n=1, 2, 3, ..., 10
Answer by greenestamps(13198) About Me  (Show Source):
You can put this solution on YOUR website!


Your question is phrased in an unusual way; I'm not sure what you are really asking.

The n-th term of the given sequence is 7n+5.

The sum of n terms of the sequence is the number of terms, times the average of the first and last terms:

S%28n%29+=+n%28%2812%2B%287n%2B5%29%29%2F2%29

The sum of 10 terms is then

S%2810%29=+10%28%2812%2B75%29%2F2%29+=+5%2887%29+=+435

But it appears from the way you have posted the question that you want to calculate not only S(10) but also S(1), S(2), ..., and S(9). If that is really what you want, then you can use the formula shown for S(n) to do the calculations.