Question

4xy-[(x²+5xy-y²)-(x²+3xy-2y²)]，其中x等于-1/4，y等于-1/2。

Answer 1

=4xy-[x²+5xy-y²-x²-3xy+2y²]
=4xy-2xy-y²
=2xy-y²
=2*（-1/4）*（-1/2）-（-1/2）²
=0

追问

我再问一下。

把x等于-1/4，y等于-1/2怎么代入到2xy-y²

Answer 2

4xy-[(x²+5xy-y²)-(x²+3xy-2y²)]
=4xy-x²-5xy+y²+x²+3xy-2y²
=2xy-y²
=2×(-1/4)×(-1/2)-(-1/2)×(-1/2)
=1/4-1/4
=0

Answer 3

=4xy-x^2-5xy+y^2-x^2-3xy+2y^2
=-4xy-2x^2+3y^2
=-1/2-1/8+3/4
=9/8

追答

是=1/8

Answer 4

追答

错了

答案是0