a4+b4+c4-2*a2b2-2*b2c2-2c2a2
=a^4+2a²b²+b^4-2(a²+b²)c²+c^4-4a²b²
=(a²+b²)²-2(a²+b²)c²+c^4-4a²b²
=(a²+b²-c²)²-4a²b²
=(a²+b²-c²+2ab)(a²+b²-c²-2ab)
=[(a+b)²-c²][(a-b)²-c²]
=(a+b+c)(a+b-c)(a-b+c)(a-b-c)
=(a^4+2a²b²+b^4)-4a²b²-2a²c²-2b²c²+c^4
=(a²+b²)²-2c²(a²+b²)+c^4-4a²b²
=(a²+b²-c²)-(2ab)²
=(a²+2ab+b²-c²)(a²-2ab+b²-c²)
=[(a+b)²-c²][(a-b)²-c²]
=(a+b+c)(a+b-c)(a-b+c)(a-b-c)
等于a4-2a2b2+b4+c4-2c2a2
=(a2-b2)的平方+c2(c2-2a2)