а) (x+y-2)-1==x+y-2-1=x+y-3
2)x+(y-x)=x+y-x=y
3)(x+y)-(x-y) =x+y-x+y=2y
4)(x+y)-(x-y) =2y
6)(x-y+2)-(x+y-2)=x-y+2-x-y+2=-2y+4
а) (x+y-2)-1==x+y-2-1=x+y-3
2)x+(y-x)=x+y-x=y
3)(x+y)-(x-y) =x+y-x+y=2y
4)(x+y)-(x-y) =2y
6)(x-y+2)-(x+y-2)=x-y+2-x-y+2=-2y+4