题目中2C方A少了个“方”吧
2B^2C^2+2C^2A^2+2A^2B^2-A^4-B^4-C^4
=4B^2C^2-(A^4+B^4+C^4+2B^2C^2-2A^2B^2-2A^2C^2)
=(2BC)^2-(A^2-B^2-C^2)^2
=(2BC+A^2-B^2-C^2)(2BC+B^2+C^2-A^2)
=[A^2-(B-C)^2][(B+C)^2-A^2]
=(A+B-C)(A-B+C)(A+B+C)(B+C-A)