x-2/3=0
y+1=0
∴x=2/3
y=-1

1/2x-2(x-1/3y^2)+(1/3y^2-3/2x)
=1/2x-2x+2/3y²+1/3y²-3/2x
=y²-3x
=(-1)²-3×2/3
=1-2
=-1