(1) 原式=(2xy-x^2-y^2)(2xy+x^2+y^2)
=-(x+y)^2(x+y)^2
=-(x+y)^4
（3）(a-b)^(n+2)-(a-b)^n
=(a-b)^n·(a-b)^2-(a-b)^n
=(a-b)^n·[(a-b)^2-1]
=(a-b)^n·(a-b-1)(a-b+1)
(4)原式=（x-2y）(x+2y)+x+2y
=(x+2y)(x-2y+1)
(5)原式=x^2+3x+2+1/4
= x^2+3x+9/4
=( x+3/2)
(1) 原式=(2xy-x^2-y^2)(2xy+x^2+y^2)
=-(x+y)^2(x+y)^2
=-(x+y)^4
（3）(a-b)^(n+2)-(a-b)^n
=(a-b)^n·(a-b)^2-(a-b)^n
=(a-b)^n·[(a-b)^2-1]
=(a-b)^n·(a-b-1)(a-b+1)
(4)原式=（x-2y）(x+2y)+x+2y
=(x+2y)(x-2y+1)
(5)原式=x^2+3x+2+1/4
= x^2+3x+9/4
=( x+3/2)