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a fost răspuns

calculati: 10+20+30+...+2020-9-18-27-...-1818

Răspuns :

Rayzen
10+20+30+...+2020-9-18-27-...-1818=
=10(1+2+3+..+202) - 9(1+2+3+...+1818:9) =

[tex]=10* \frac{202*203}{2} -9* \frac{202*203}{2} = \frac{202*203}{2}*(10-9)= \frac{202*203}{2}=101*203 = \\ =(100+1)*203 = 203*100 + 203*1 = 20300+203 = 20503[/tex]

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