a) 1-2+3-4+5-6+...+49-50
Le grupam A={1-2;3-4;5-6;...;49-50}, rezultand faptul ca toate grupele dau -1, asadar rezultatul ar fi=-1×card A
card A=card B, unde B={-2;-4;-6;...;-50}
card B=50:2+1-1=25
1-2+3-4+5-6+...+49-50=-1×25=-25
b) -1-2-3-...-49-50=
-1(1+2+3+...+49+50)=
-1(50×51:2)=
-1(25×51)
-1275
