X+1/8=3/5; x-3/7=4/21

Найдем переменную в простом линейном уравнении с дробями:

1. x + 1/8 = 3/5;

x = 3/5 - 1/8;

Приводим к общему знаменателю;

x = (8 * 3) / (5 * 8) - (5 * 1) / (8 * 5);

x = 24/40 - 5/40;

x = 19/40;

Проверим:

19/40 + 1/8 = 3/5;

19/40 + (5 * 1) / (8 * 5) = 3/5;

19/40 + 5/40 = 3/5;

24/40 = 3/5;

3/5 = 3/5;

Все верно;

2. x - 3/7 = 4/21;

x = 4/21 + 3/7;

x = 4/21 + (3 * 3) / (7 * 3);

x = 4/21 + 9/21;

x = 13/21;

Проверим:

13/21 - 3/7 = 4/21;

13/21 - (3 * 3) / (7 * 3) = 4/21;

13/21 - 9/21 = 4/21;

4/21 = 4/21;

Все верно.