soluzione
Scomporre
x
2
- xy + y
2
+ x
3
+ y
3
=
= (x
2
- xy + y
2
) + (x
3
+ y
3
) =
= (x
2
- xy + y
2
) + (x + y)(x
2
- xy + y
2
) =
= (x
2
- xy + y
2
)[1 + (x + y)] =
= (x
2
- xy + y
2
)(1 + x + y)