数学高手过来：很难的因式分解

1.x^3-3x^2+4
=(x^3-2x^2)-(x^2-4)
=x^2(x-2) -(x+2)(x-2)
=(x-2)(x^2-x-2)
=(x-2)(x+1)(x-2)
=(x+1)(x-2)^2

2.x^4+y^4+(x+y)^4
=(x^2+y^2)^2-2x^2*y^2+(x+y)^4
=[(x+y)^2-2xy]^2-2x^2*y^2+(x+y)^4
=(x+y)^4-4xy*(x+y)^2+4x^2*y^2-2x^2*y^2+(x+y)^4
=2(x+y)^4-4xy*(x+y)^2+2x^2*y^2
=2[(x+y)^2-xy]^2
=2(x^2+xy+y^2)^2

3.(x+y)(x+y+2xy)+x^2*y^2－1
=(x+y)^2+2xy(x+y)+x^2*y^2－1
=(x+y+xy)^2 -1
=(x+y+xy+1)(x+y+xy-1)

4.(x－a)(x－2a)(x－3a)(x－4a)－120a^4
=[(x-a)(x-4a)]*[(x-2a)(x-3a)]-120a^4
=[(x^2-5a+4a^2)*(x^2-5a+6a^2)]-120a^4
=(x^2-5a)^2+10(x^2-5a^2)+24a^4-120a^4
=(x^2-5a)^2+10(x^2-5a^2)-96a^4
=(x^2-5a-6a^2)*(x^2-5a+16a^2)
=(x+a)(x-6a)(x^2-5a+16a^2)

太多了

1、（x+1）（x-2）^2

#￥%￥#·%#￥·%楼上的有错！
第三题没有分解完
应该是(x+1)(y+1)(x+y+xy-1)
其他与James_knows答案一样
1.x^3-3x^2+4
=x^2(x-2) -(x+2)(x-2)
=(x+1)(x-2)^2

2.x^4+y^4+(x+y)^4