问题
解答题
化简求值:x2-2(x2-3xy)+3(y2-2xy)-2y2,其中x=
|
答案
x2-2(x2-3xy)+3(y2-2xy)-2y2
=x2-2x2+6xy+3y2-6xy-2y2
=-x2+y2,
当x=
,y=-1时,1 2
原式=-(
)2+(-1)21 2
=-
+11 4
=
.3 4
化简求值:x2-2(x2-3xy)+3(y2-2xy)-2y2,其中x=
|
x2-2(x2-3xy)+3(y2-2xy)-2y2
=x2-2x2+6xy+3y2-6xy-2y2
=-x2+y2,
当x=
,y=-1时,1 2
原式=-(
)2+(-1)21 2
=-
+11 4
=
.3 4