Решите уравнение 2/3-(7/9-а)=1/3
2/3-(7/9-а)=1/3
7/9-а=2/3-1/3
7/9-а=1/3
а=7/9-1/3
а=4/9
Проверка:
2/3-(7/9-4/9)=1/3
2/3-1/3=1/3
1/3=1/3