S=5+10+15+....................525+530+535 = (5+535)·107:2=540·107:2 = 28890
(535-5):5 +1 = 107 termeni.
Il dai pe 5 factor comun pt a avea nr consectuve de la 1. Aplici formula pt suma lui Gauss S=[n(n+1)] :2 S=5(1+2+3+...+105+106+107) S=5[107(107+1)] :2 S=5(107×108):2 S=5×5778 S=28890
