There are several math problems to be corrected! There will be extra points within today-~ urgent! ! ! - Training Enrollment Network

There are several math problems to be corrected! There will be extra points within today-~ urgent! ! !

Note: 1-2 =- 1, 3-4 =- 1, 5-5 =- 1. ........

When n is odd, sn =-1* (n-1)/2+n = (n+1)/2.

When n is an even number, Sn=-N/2.

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