先化简,再求值.-1/3（x²y²-xy+3）+2[x²-1/2（xy-2x+y-1）]+3x-1,其中x=-4
问题描述：
先化简,再求值.-1/3（x²y²-xy+3）+2[x²-1/2（xy-2x+y-1）]+3x-1,其中x=-4
答
-1/3（x²y²-xy+3）+2[x²-1/2（xy-2x+y-1）]+3x-1
=-1/3x²y²+1/3xy-1+2x²-xy+2x-y+1+3x-1
=-1/3x²y²+2x²-2/3xy+5x-y-1
把 x=-4代入,得
-16/3y²+32-8/3y-20-y-1
=-16/3y²-11/3y+11