SOLUTION: find the sum of the following arithmetic series and write in summation notation http://prntscr.com/sfiszj

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Question 1158912: find the sum of the following arithmetic series and write in summation notation
http://prntscr.com/sfiszj
Answer by MathLover1(20849) About Me  (Show Source):
You can put this solution on YOUR website!

b.
19,13,...
since you have arithmetic series, the common difference is+d=-6
the sum of first 10 terms formula is
a%5B1%5D=19
d=-6
n=10
S%5Bn%5D=%28n%2F2%29%282a%5B1%5D%2Bd%28n-1%29%29.....substitute given values
S%5B10%5D=%2810%2F2%29%282%2A19-6%2810-1%29%29
S%5B10%5D=%2810%2F2%29%2838-54%29
S%5B10%5D=%2810%2F2%29%28-16%29
S%5B10%5D=10%28-8%29
S%5B10%5D=-80

d.
a%5B1%5D=-9
d=8
n=8
S%5Bn%5D=%28n%2F2%29%282a%5B1%5D%2Bd%28n-1%29%29
S%5B8%5D=%288%2F2%29%282%28-9%29%2B8%288-1%29%29
S%5B8%5D=%288%2F2%29%28-18%2B56%29
S%5B8%5D=%288%2F2%29%2838%29
S%5B8%5D=%288%29%2819%29
S%5B8%5D=152