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a) Determinați: 6+11+16+21+.......+506
b)Efectuați: 4+9+14+19+......+1004


Răspuns :

6+11+16+21+......+506=(1+5)+(1+5*2)+(1+5*3)+(1+5*4)+.........+(1+5*101)=1*101+5+5*2+5*3+5*4+..........+5*101=101+5(1+2+3+........+101)=101+5*101*102:2=101+25755=25856