原式=(X^2)^2+(Y^2)^2+(X+Y)^4
=(X^2+Y^2)^2-2(XY)^2+(X+Y)^4
=((X+Y)^2-2XY)^2-2(XY)^2+(X+Y)^4
设X+Y=Z
原式=(Z-2XY)^2-2(XY)^2+(Z)^4
=(Z^4-4XYZ^2+4(XY)^2)-2(XY)^2+(Z)^4
=2Z^4-4XYZ^2+2(XY)^2
=2(Z^4-2XYZ^2+(XY)^2)
=2((Z^2)^2-2XYZ^2+(XY)^2)
=2(Z^2-XY)^2
=2((X+Y)^2-XY)^2
=2(X^2+Y^2+XY)^2
如果有不明白的你可以补充说明,我看见拉就回答.