In the sequence {an}, an = [(- 1) ^ (n + 1)] * (2n + 1) is used to find the first n terms and Sn of the sequence. Pay attention to the method of summation of union terms ~... This method has never been mentioned in class - 0- Pay attention to the method of summation of union terms ~... I haven't really talked about this method in class - 0-

In the sequence {an}, an = [(- 1) ^ (n + 1)] * (2n + 1) is used to find the first n terms and Sn of the sequence. Pay attention to the method of summation of union terms ~... This method has never been mentioned in class - 0- Pay attention to the method of summation of union terms ~... I haven't really talked about this method in class - 0-

The sequence is 1 - 3 5 - 7. (2n + 1) with n numbers
The sum of the two terms is (the sum of the even term and the technical terms next to it, such as 1-3) - 2
If a sequence has even terms (2n terms), then Sn = n * (- 2) = - 2n
If the sequence has an odd term (2n + 1), then the sum of the first 2n is - 2n, and then add the 2n + 1 term
Sn=-2n+(-1)^(n+1)]*(2n+1)
If I don't get it, I'll write it
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