1.(a²-b²)²+（a²+2b²)²
=2a^4+2a²b²+5b^4
=不能分解因式了
2.3a-12a²+18a³
=3a(1-4a+6a²)
3.(x+y)²(x-y)-(x+y)(x-y)²
=(x+y)(x-y)(x+y-x+y)
=2y(x+y)(x-y)
4.x²y²-x²-y²+1
=x²(y²-1)-(y²-1）
=(y²-1)(x²-1)
=(y+1)(y-1)(x+1)(x-1)
5.x²-2x-4y²-4y
=x²-4y²-2x-4y
=(x+2y)(x-2y)-2(x+2y)
=(x+2y)(x-2y-2)
6.(a²-2b²+4）（a²+2b²-4）