先化简,后求值:4xy-(2x2+5xy-y2)+2(x2+3xy),其中|x+2|+(y−12)
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先化简,后求值:4xy-(2x2+5xy-y2)+2(x2+3xy),其中|x+2|+(y−
)
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![先化简,后求值:4xy-(2x2+5xy-y2)+2(x2+3xy),其中|x+2|+(y−12)](/uploads/image/z/8756709-69-9.jpg?t=%E5%85%88%E5%8C%96%E7%AE%80%EF%BC%8C%E5%90%8E%E6%B1%82%E5%80%BC%EF%BC%9A4xy-%EF%BC%882x2%2B5xy-y2%EF%BC%89%2B2%EF%BC%88x2%2B3xy%EF%BC%89%EF%BC%8C%E5%85%B6%E4%B8%AD%7Cx%2B2%7C%2B%28y%E2%88%9212%29)
4xy-(2x2+5xy-y2)+2(x2+3xy),
=4xy-2x2-5xy+y2+2x2+6xy),
=5xy+y2,
∵
.
x+2
.+(y-
1
2)2=0
∴x=-2,y=
1
2
当x=-2,y=
1
2时,代入上式得:
原式=5xy+y2,
=5×(-2)×
1
2+(
1
2)2
=−4
3
4
=4xy-2x2-5xy+y2+2x2+6xy),
=5xy+y2,
∵
.
x+2
.+(y-
1
2)2=0
∴x=-2,y=
1
2
当x=-2,y=
1
2时,代入上式得:
原式=5xy+y2,
=5×(-2)×
1
2+(
1
2)2
=−4
3
4
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