А)1/2+х=5/6
х=5/6-1/2
х=5/6-3/6
х=2/6
х=1/3
1/2+1/3=5/6
3/6+2/6=5/6
5/6=5/6
б)а+1/4=3/4
а=3/4-1/4
а=2/4
а=1/2
1/2+1/4=3/4
2/4+1/4=3/4
3/4=3/4
в)у-1/5=3/10
у=3/10+1/5
у=3/10+2/10
у=5/10
у=1/2
1/2-1/5=3/10
5/10-2/10=3/10
3/10=3/10
г)5/6-с=1/3
с=5/6-1/3
с=5/6-2/6
с=3/6
с=1/2
5/6-1/2=1/3
5/6-3/6=1/3
2/6=1/3
1/3=1/3