\(\dfrac{x^3y+xy^3+xy}{x^3+y^3+x^2y+xy^2+x+y}\)=\(\dfrac{xy\left(x^2+y^2\right)+xy}{\left(x+y\right)\left(x^2-xy+y^2\right)+xy\left(x+y\right)+\left(x+y\right)}\)
=\(\dfrac{xy\left(x^2+y^2+1\right)}{\left(x+y\right)\left(x^2+y^2+1\right)}=\dfrac{xy}{x+y}\)