(x4次方+y4次方)-(2x平方y平方)平方
=(x^4+y^4+2x²y²)(x^4+y^4-2x²y²)
=(x²+y²)²(x²-y\x0d²)²
=(x²+y²)²(x+y)²(x-y)²
-4xy-4x平方-y平方
=-(4x²+4xy+y²)
=-(2x+y)²