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cat face 2+4+6+...+240?

Răspuns :

[tex]\displaystyle 2+4+6+...+240=2(1+2+3+...+120)=2 \times \frac{120(120+1)}{2} = \\ \\ =2\times \frac{120 \times 121}{2} =\not2 \times \frac{14520}{\not2} =14520[/tex]