6/3 х + 12/4 под всем этим дробная черта 7 и равно 3

(6/3 х + 12/4) / 7 = 3,

1) 6/3 х = 2 х,

2) 12/4 = 3.

(6/3 х + 12/4) / 7 = 3,

(2 х + 3) / 7 = 3,

7 * ((2 х + 3) / 7) = 3 * 7,

(2 х + 3) = 21,

2 х + 3 = 21,

2 х = 21 - 3,

2 х = 18,

х = 18 : 2,

х = 9.

Проверка: ((6/3) * 9 + 12/4) / 7 = 3,

(2 * 9 + 3) / 7 = 3,

(18 + 3) / 7 = 3,

21/7 = 3,

3 = 3.

2) Если х под дробной чертой тогда

(6/3 х + 12/4) / 7 = 3,

(2/х + 3) / 7 = 3,

7 * ((2/х + 3) / 7) = 3 * 7,

2/х + 3 = 21,

2/х = 21 - 3,

2/х = 18,

18 х = 2,

х = 2 : 18,

х = 1/9.

Проверка: (6 / (3 * 1/9) + 12/4) / 7 = 3,

(6 / (3/9) + 3) / 7 = 3,

((6*9) / 3 + 3) / 7 = 3,

(54/3 + 3) / 7 = 3,

(18 + 3) / 7 = 3,

21/7 = 3,

3 = 3.