1.(a²+b²)^2-4a²b²=a^4+b^4+2a^2b^2-4a^2b^2=a^4+b^4-2a^2b^2=(a^2-b^2)^2=(a+b)^2(a-b)^2
2.2y(x-y)²-(y-x)的三次方=(x-y)^2(2y-y+x)=(x-y)^2(x+y)
3.（m-n）的三次方+3（n-m）²-n（m-n）²=(m-n)^2(m-n+3-n)=(m-n)^2(m-2n+3)
4.2acd-c²a-ad²=a(2cd-c^2-d^2)=-a(c^2-2cd+d^2)=-a(c-d)^2