Funktionenkörper/2 Variablen/Rechnung/Aufgabe

Berechne in ${}\mathbb {Q} (X,Y)$

{\frac {7X^{2}-XY^{3}+Y^{4}}{5X-{\frac {1}{3}}Y^{4}}}\cdot {\frac {1}{X^{2}Y^{3}}}+{\frac {3X^{3}+X^{2}Y^{2}-XY^{2}}{2+4X^{3}-X^{257}}}\cdot {\frac {1}{X^{2}Y^{3}}}-{\frac {1}{7}}X^{3}+XY+Y^{6}+9