Question

Calculati 3*(1+2+3+......+1000)+(3+4+5+......+1000)*(-3)

Answer 1

Aplicam cunoscuta formula SUMA LUI GAUSS:
3*(1+2+3+...+1000)+(3+4+5+...+1000)*(-3)=
3*($\frac{1000*1001}{2}$)+[(1+2+3+4+5+...+1000)*(-3)-(1+2)]=
3*(500*1001)+($\frac{1000*1001}{2}$*(-3)-3]=
3*500500+[500*1001*(-3)-3]=
1501500+(-1501500-3)=
1501500+(-1501503)=
1501500-1501503=
-3