11.
5x+1 = 3x+1
5x-3x = 1-1
2x = 0
x = 0:2
x= 0
12.
6x -1 = 11
6x = 11+1
6x = 12
x = 12:6
x = 2
13.
x-1 = 7(x-1)
x-1 = 7x-7
x-7x = -7+1
-6x = -6
6x = 6
x = 6:6
x = 1
14.
x-2 = 1+4x
x-4x = 1+2
-3x = 3
3x = -3
x = -3:3
x = -1
15.
5x+5 = 5(x-1)
решений нет