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Efectuati: x+2x+3x+....+9x

Răspuns :

[tex]x+2x+3x+...+9x =\ \textgreater \ x(1+2+3+....9)~ Obtinem: x* \frac{n(n+1)}{2} [/tex][tex]x* \frac{9*10}{2} =x*45=\ \textgreater \ Suma~e~egala~cu: 45x[/tex]