原式= 1 2 x-2x+ 2 3 y- 3 2 x+ 1 3 y=( 1 2 -2- 3 2 )x+( 2 3 + 1 3 )y=-3x+y,当x=-2,y= 2 3 时,原式=-3×(-2)+ 2 3 = 20 3 .