1.（-2ab²）·（3a²b-2ab-1）
=-6a³b³+4a²b³+2ab²
2.4(a-b)²-（2a+b)（-b+2a)
=4(a²-2ab+b²)-(4a²-b²)
=-8ab+5b²
3.(x-1/2)²(1/2+x)
=(x-1/2)(x-1/2)(x+1/2)
=(x-1/2)(x²-1/4)
=x³-1/2x²-1/4x+1/8
4.(1+x-y)(x+y-1)
=[x-(y-1)](x+y-1)
=x²-(y-1)²
=x²-y²+2y-1
5 999²-1002*998
=(1000-1)²-(1000+2)×(1000-2)
=1000²-2000+1-1000²+4
=-1995
6 x²+y²=(x+y)²-2xy=4²-6=10
(x-y)²=x²+y²-2xy=10-6=4
则x-y=2或-2
7 x的四次方-2x²+1=(x²-1)²=[(x+1)(x-1)]²=(x+1)²(x-1)²
8 （x²-3）-12（x²-3）+36=(x²-3-6)²=[(x+3)(x-3)]²=(x+3)²(x-3)²