x^6-3x^4y^2+3x^2y^4-y^6 设x^2=A y^2=B A^3-3A^2B+3AB^2-B^3 =( A^3-B^3)+(-3A^2B+3AB^2) =(A-B)(A^2+AB+B^2)-3AB(A-B) =(A-B)^3 带入上式子得（x^2-y^2）^3 =[(x+y)(x-y)]^3
