5х+(3х+7)=8х+7
8а+(1-3а)=8а+1-3а=
=5а+1
-у+(у-1)= -у+у-1= -1
-5m+( -m-n)=
-5m-m-n= -6m-n
2x-3y+( -y -x)=
2x-3y-y-x= x-4y