( x" + y" )" - 4x"y"
= ( x" + y" )" - ( 2xy )"
= ( x" - 2xy + y" )( x" + 2xy + y" )
= ( x - y )"( x + y )"
或者
= x^4 + 2x"y" + y^4 - 4x"y"
= x^4 - 2x"y" + y^4
= ( x" - y" )"
= ( x - y )"( x + y )"
( x" + y" )" - 4x"y"
= ( x" + y" )" - ( 2xy )"
= ( x" - 2xy + y" )( x" + 2xy + y" )
= ( x - y )"( x + y )"
或者
= x^4 + 2x"y" + y^4 - 4x"y"
= x^4 - 2x"y" + y^4
= ( x" - y" )"
= ( x - y )"( x + y )"