我也是初高中衔接的.
1.原式=a^4-(2b^2+2c^2)a^2+b^4+c^4-2b^2c^2
=a^4-(2b^2+2c^2)a^2+(b^2-c^2)^2
=a^4-(2b^2+2c^2)a^2+(b+c)^2(b-c)^2
=[a^2-(b+c)^2][a^2-(b-c)^2]
=(a-b-c)(a+b+c)(a-b+c)(a+b-c)
2.原式=x^2+(1-4y)x+4y^2-2y-6
=x^2+(1-4y)x+2(2y-3)(y+1)
=(x-2y+3)(x-2y-2)
3.原式=x^2+(y+5)x-(3y-4)(2y-9)
=(x-2y+9)(x+3y-4)
4.原式=x^3-x^2+x^2-3x+2
=x^2(x-1)+(x-1)(x-2)
=(x-1)(x^2+x-2)
=(x-1)^2(x+2)
如果楼主还有什么不懂的话可以尽管问我.