(2x-y)的四次方-(2x+y)的四次方=[(2x-y)²+(2x+y)²]*[(2x-y)²-(2x+y)²]=[4x²-4xy+y²+4x²+4xy+y²]*[4x²-4xy+y²-4x²-4xy-y²]=(8x²+2y²)(-8xy)=-16xy(4x²+y²)
