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11+22+33+....7700= faceti cu formula lui gaoss ca eu am uitat cum se face

Răspuns :

11(1+2+3+...+700)=11x(701x700):2=(11x490700):2=2698850
11+22+33+.........................+7700=    ( dam factor comun  110
11x(1+2+3+........................+700)=      (aplicam formula S=nx(n+1):2   )
11x[700x(700+1):2]=
11x[700x701:2]=
11x(490.700:2)=
11x245.350=2.698.850