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Aflati suma nr.
3 + 6 + 9 + 12 +............ + 99
5 + 10 + 15 + ...................... + 2005


Răspuns :

3+6+9+.....+99=3(1+2+3+.....33)=3*(1+33)*33/2=3*34*33/2=1683


5+10+.....+2005=5(1+2+3+....+401)=5*(1+401)*401/2=403005
3+6+9+12+...+99=3×(1+2+3+...33)=3×[tex] \frac{33*34}{2} [/tex]=1683
5 + 10 + 15 + ... + 2005 =5×(1+2+3+...401)=5×[tex] \frac{401*402}{2} [/tex]=403005