помогите решить х+(y-z)= х+(-y-z)= -(y-z)-x= (c-d)-(a-b)-(b-c)=
х+(y-z)=х+у-z
х+(-y-z)=x-y-z
-(y-z)-x=-y+z+x
(c-d)-(a-b)-(b-c)=c-d-a+b-b+c=2c-d-a