SOLUTION: find the sum of each arithmetic series -4+1+6+...+91 13+20+27+...+272 89+86+83+...+20 8+11+14+...+23

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Question 612242: find the sum of each arithmetic series
-4+1+6+...+91
13+20+27+...+272
89+86+83+...+20
8+11+14+...+23
Answer by ewatrrr(24785) About Me  (Show Source):
You can put this solution on YOUR website!
 

Hi, 

find the sum of each arithmetic series:  

Note: a%5Bn%5D=a%5B1%5D%2B%28n-1%29%2Ad  and S%5Bn%5D=%28n%28a%5B1%5D%2Ba%5Bn%5D%29%29%2F2

 highlight%28-4%29 +1+6+...+ highlight%2891%29    || d= 5 

91 = -4 + (n-1)5 

n = 20 

S%5Bn%5D=%28n%28-4%2B+91%29%29%2F2=+%2887n%29%2F2+=+870 

13+20+27+...+272  ||d = 7

89+86+83+...+20   ||d = -3

8+11+14+...+23    ||d = 3