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a fost răspuns

7+14+21+...+2002=.......................................................................Mai e putin si am terminat

Răspuns :

[tex]7( 1+2+3+...+ 286) = 7 * \frac{ [ (1+286)*286]}{2} = 287,287[/tex]
[tex]\displaystyle 7+14+21+...+2002=7(1+2+3+...+286)= \\ \\ =7 \times \frac{286(286+1)}{2} =7 \times \frac{286 \times 287}{2} =7 \times \frac{82082}{2} = \\ \\ =7 \times 41041=287287[/tex]

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