Question

Find the sum to nth terms 1-2+3-4+5-6+...

Answer 1

S(n) =  1 - 2 + 3 - 4 + 5 - 6 .... n terms

S(n=1) = 1      S(2) = -1         S(3) = 2
S(4) = -2         S(5)= 3            S(6) = -3

S(2k - 1) = k       S(2k)= - k     k= 1,2,3 ....

S(n) =  (n+1)/2   if n is odd
        =  - n/2       if n is even.