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Determina nr natural X pt care
7×X+14×X+21×x+28×X+.....+126×X=7×9×19


Răspuns :

7×X+14×X+21×x+28×X+.....+126×X=7×9×19
se da factor comun 7 ori X
7×X( 1 + 2 + 3 + 4 +...+ 18) = 7 × 9 × 19

7×X × 18 × (18+1) : 2 = 7 × 9 × 19

7 × X × 9 × 19 = 7 × 9 × 19

X = 1