1) 5+10+15+20+........+1000= factor comun 5
5x(1+2+3+4+..........+200)= aplicam formula sumei Gauss
5x[200x(200+1):2]=
5x[200x201:2]=
5x(40200:2)=
5x20100=100500
2) 8+16+24+32+...............+4000= factor comun 8
8x(1+2+3+4+................+500)= aplicam formula sumei Gauss
8x[500x(500+1):2]=
8x[500x501:2]=
8x(250500:2)=
8x125250=1002000
3) 11+22+33+44+55+.................7700= factor comun 11
11x(1+2+3+4+5+....................+700)= aplicam formula sumei Gauss
11x[700x(700+1):2]=
11x[700x701:2]=
11x(490700:2)=
11x245350=2698850