-1/2x+2(x-1/3y²)-(-3/2x+1/3y²),
=-1/2x+2x-2/3y^2+3/2x-1/3y^2
=3x-y^2
将x=2,y=2/3代入,得
=3*2-(2/3)^2
=6-4/9
=5又5/9=50/9