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Calculati
x+2x+3x+4x+.........20x



Răspuns :

Renatemambouko
x+2x+3x+4x+.........20x =
=x(1+2+3+4+....+20)=x*20*(20+1)/2=210x
[tex]\displaystyle x+2x+3x+4x+...+20x=x(1+2+3+...+20)= \\ \\ =x \cdot \frac{20(20+1)}{2} =x \cdot \frac{20 \cdot 21}{2} =x \cdot \frac{420}{2} =x \cdot 210=210x[/tex]

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