12x-x=55. 2(x+3)=16. 5(x+3)+7=3(x+12)

Найдем корень уравнения.

1) 12 * x x = 55;

Вынесем за скобки х.

x * (12 1) = 55;

x * 11 = 55;

11 * x = 55;

x = 55/11;

x = 5.

2) 2 * (x + 3) = 16;

Раскроем скобки.

2 * x + 2 * 3 = 16;

2 * x + 6 = 16;

2 * x = 16 6;

2 * x = 10;

x = 10/2;

x = 5.

3)  5 * (x + 3) + 7 = 3 * (x + 12);

5 * x + 5 * 3 + 7 = 3 * x + 3 * 12;

5 * x + 15 + 7 = 3 * x + 36;

5 * x + 22 = 3 * x + 36;

5  * x 3 * x = 36 22;

2 * x = 14;

x = 14/2;

x = 7.