Răspunsuri

2014-03-05T13:57:27+02:00
Daca n e par:
(1*1-2*2)+.... +((n-1)*(n-1)-n*n)=
-1-2-3-4-....-(n-1)-n= -n(n+1)/2
daca n e impar:
1*1-2*2+.....-(n-1)*(n-1)+n*n=
(n*n-(n-1)*(n-1))+.... + (3*3-2*2)+1*1= n+(n-1)+.... + 3+2+1= n(n+1)/2