Решите уравнение 1) x+4/21=2/3+2/7 2) y+1/4=4/5-3/10 3) (4/5-x)+13/20=7/10

 1)
x+4/21=2/3+2/7
x+4/21=14/21+6/21
x+4/21 = 20/21
x=20/21-4/21
x=16/21

2)
y+1/4=4/5-3/10
y+1/4=8/10-3/10
y+1/4=5/10
y=1/2-1/4
y=2/4-1/4
y=1/4

3)
(4/5-x)+13/20=7/10
4/5-x=7/10-13/20
4/5-x = 14/20-13/20
4/5-x=1/20
x=4/5-1/20
x=16/20-1/20
x=15/20
x=3/4