2 6/11+(7-а)=4 2/11
7-а=4 2/11-2 6/11
7-а=3 13/11-2 6/11
7-а=1 7/11
7-1 7/11=а
6 11/11-1 7/11=а
5 4/11=а
Проверка
2 6/11+(7-5 4/11)=4 2/11
2 6/11+(6 11/11-5 4/11)=4 2/11
2 6/11+1 7/11=4 2/11
3 13/11=4 2/11
4 2/11=4 2/11
2 6/11+(7-а)=4 2/11
7-а=4 2/11-2 6/11
7-а=3 13/11-2 6/11
7-а=1 7/11
7-1 7/11=а
6 11/11-1 7/11=а
5 4/11=а
Проверка
2 6/11+(7-5 4/11)=4 2/11
2 6/11+(6 11/11-5 4/11)=4 2/11
2 6/11+1 7/11=4 2/11
3 13/11=4 2/11
4 2/11=4 2/11