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4+8+12+....400=?     este de clasa 5

Răspuns :

[tex]4+8+12+...+400= \\\\ =4(1+2+3+...+100)= \\\\ =4*\frac{1+100}{2}*100= \\\\ = 2*101*100= \\\\ = \boxed{20200}[/tex]