P - Q = (1/3х - 1/3y) - (x+2y) - (1/3x + 1/3y - (x-y)) =
= 1/3x-1/3y -x -2y -1/3x -1/3y +x -y = x*(1/3-1-1/3+1) - y(1/3+2+1/3+1)=
= -3 2/3 y
P - Q = (1/3х - 1/3y) - (x+2y) - (1/3x + 1/3y - (x-y)) =
= 1/3x-1/3y -x -2y -1/3x -1/3y +x -y = x*(1/3-1-1/3+1) - y(1/3+2+1/3+1)=
= -3 2/3 y