确定最后一项是- 这样的话没法分解啊,我下面按照+分解,不明白欢迎追问!
利用换元法
设x+y=a,x-y=b,则
(x+y)^4+(x^2-y^2)^2+(x-y)^4
=a⁴+(ab)²+b⁴
=a⁴+2a²b²+b⁴-a²b²
=(a²+b²)²-(ab)²
=(a²+b²+ab)(a²+b²-ab)
=[(x+y)²+(x-y)²+(x+y)(x-y)][(x+y)²+(x-y)²-(x+y)(x-y)]
=(x²+2xy+y²+x²-2xy+y²+x²-y²)(x²+2xy+y²+x²-2xy+y²-x²+y²)
=(3x²+y²)(x²+3y²)