解:
(x+y)^2-(x^3+y^3)/(x+y)
=(x+y)^2-[(x+y)(x^2-xy+y^2)]/(x+y)
=(x+y)^2-[x^2-xy+y^2]
=x^2+y^2+2xy-x^2+xy-y^2
=3xy