1.
因为x3+y3+z3-3xyz=(x+y+z)(x2+y2+z2-xy-yz-xz)
所以看成
x3-（2y）3-z3-3x2yz=()(x-2y-z)(x2+4y2+z2+2xy-2yz+xz)
2.a^7-a^5b²+a²b^5-b^7
=a5(a2-b2)+b5(a2-b2)
=(a5-b5)(a+b)(a-b)