(12/17+у)-5/8=3/8
12/17+у=3/8+5/8
12/17+у=1
у=1-12/17
у=5/17
Проверка
(12/17+5/17)-5/8=3/8
1-5/8=3/8
3/8=3/8
(12/17+у)-5/8=3/8
12/17+у=3/8+5/8
12/17+у=1
у=1-12/17
у=5/17
Проверка
(12/17+5/17)-5/8=3/8
1-5/8=3/8
3/8=3/8