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X+2x+3x+...+69x =?
Va rog !


Răspuns :

=69x *70x :2
=69x *35x
=2415x
(folosesti suma GAUSS:1+2+3+...+n=n x (n+1):2)
X+2x+3x+...+69x =x(1+2+3+.....+69)=


(1+2+3+.....+69) =suma Gauss, incepe din 1 si nr sunt consecutive
are formula de calcul :[n(n+1)]:2
adica [69(69+1)]:2=(69×70):2=69×35=2415


x+2x+3x+...+69x =2415x