先化简,再求值 ：(xy-3x^2)-2(xy-2x^2-1),其中x、y满足条件丨x+2丨+（y-1）^2=0

题目

先化简,再求值 ：(xy-3x^2)-2(xy-2x^2-1),其中x、y满足条件丨x+2丨+（y-1）^2=0

答案

丨x+2丨+（y-1）^2=0
丨x+2丨=0,（y-1）^2=0
x+2=0,y-1=0
x=-2,y=1
所以
(xy-3x^2)-2(xy-2x^2-1)
=(xy-3x^2)-2xy+4x^2+2
=-xy+x^2+2
=-(-2)×1＋（-2）^2+2
=2+4+2
=8