John M. answered • 03/22/14
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Analytical assistance -- Writing, Math, and more
Dalia, I think you're looking at something like this
26
Σ(-1)n2n
n=0
There are two parts to this summation. First, consider (-1) to the n. When n is even (ie 0,2,4, ...,26) it equals 1, and when it's odd (ie 1,3,5, ..., 25) it equals -1. Then consider 2n. When n=0, it equals 0, when 1, 2 and ... N=26, it equals 52. Putting it together you get
0,-2,4,-6,... , -50,52
I'll leave the adding to you.
Dalia S.
thank you but what do i have to add?
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03/23/14
John M.
You add each value of the series so
0+(-2)+4+(-6)+8+ ... +48+(-50)+52
Steve's point about grouping the numbers to see if there is a pattern as you add each term is a good idea.
When n=0, the series S(0)=0
when n=1, S(1)=0-2=-2
S(2)=0-2+4=2
S(3)=0-2+4-6=-2
S(4)=0-2+4-6+8=2
... [whats the pattern?]
S(25)=???
S(26)=???
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03/23/14
Steve S.
03/22/14