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determina nr natural X pt care 7X+14X+21X+28X+.....+126X=7ori9ori19
ma poate ajuta cineva?


Răspuns :

7X+14X+21X+28X+.....+126X=7×9×19

7x(1 + 2 + 3 + 4 +...+ 18) = 7 × 9 × 19

7x × 18 × 19 : 2 = 7 × 9 × 19

7x × 9 × 19 = 7 × 9 × 19

x = 1