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Cum se rezolva
5+10+15+...+625


Răspuns :

5+10+15+...+625 =5(1+2+3....+125)=5 x 125 x(125+1)/2=5x125x63=39375
[tex]5+10+15+...+625=5(1+2+3+...+125)= \\ =5* \frac{125(125+1)}{2} =5* \frac{125*126}{2} =5* \frac{15750}{2} =5*7875=39375[/tex]