SOLUTION: Find the sum of the arithmetic sequence. 3/2 + 1/2+...+(-11/2)

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Question 1039414: Find the sum of the arithmetic sequence.
3/2 + 1/2+...+(-11/2)
Answer by Fombitz(32388) About Me  (Show Source):
You can put this solution on YOUR website!
Look at the sequence
a
a-2
a-4%7D%7D%0D%0A%7B%7B%7Ba-6
a-8
5 terms starting with a, each successive term removes 2.
The sum would be,
S=a%2Ba-2%2Ba-4%2Ba-6%2Ba-8
S=5a-20
S=5%28a-4%29
or in terms of the number of values,
S=5%28a-4%29=n%28a-%28n-1%29%29=n%28a%2B1-n%29
So in your sequence,
3%2F2%2B1%2F2-1%2F2-3%2F2-5%2F2-7%2F2-9%2F2-11%2F2=%281%2F2%29%283%2B1-1-3-5-7-9-11%29
The starting term is a=3 and n=8,
so then,
S=%281%2F2%298%283%2B1-8%29
S=4%284-8%29
S=4%28-4%29
S=-16