数学数学数学，初二数学~

1.（xy^2+3)(xy^2+3)-2x(-x+y)
=x^y^4+6xy^2+9+2x^2-2xy

2.(x+2)(x^2+4)(x-2)
=[(x+2)(x-2)](x^2+4)
=(x^2-4)(x^2+4)
=x^4-16

3.先化简，再求值。
(x^2y^2-4)(-x^2y^2-4)-4(xy-1/2)*(xy-1/2),其中x=1,y=-2

原式=- (x^2y^2-4)(x^2y^2+4)-4(xy-1/2)*(xy-1/2)
=-(x^4y^4-16)-4(x^2y^2-xy+1/4)
=-x^4y^4+16-4x^2y^2+4xy-1
=-x^4y^4-4x^2y^2+4xy+15
再把x,y代入，得到原式=-16-16-8+15=-25

1.
9 + 2 x^2 - 2 x y + 6 x y^2 + x^2 y^4

2.
-16 + x^4

3.
15 + 4 x y - 4 x^2 y^2 - x^4 y^4
-25