\((x-y)^{3}-x^{3}+y^{3}=(x-y)^{3}-(x^{3}-y^{3})\)

\(=(x-y)^{3}-(x-y)(x^{2}+xy+y^{2})\)

\(=(x-y)\{ (x-y)^{2}-(x^{2}+xy+y^{2})\}\)

\(=(x-y)(x^{2}-2xy+y^{2}-x^{2}-xy-y^{2})\)

\(=-3xy(x-y)\) ………（答）