Berechne in ${\displaystyle {}\mathbb {Q} (X)}$ die folgenden Ausdrücke.

1. Das Produkt

   ${\displaystyle {\frac {2X^{3}-5X^{2}+X-1}{X^{2}-2X+6}}\cdot {\frac {X^{2}+3}{5X^{3}-4X^{2}-7}}.}$

2. Die Summe

   ${\displaystyle {\frac {4X^{3}-X^{2}+6X-2}{X^{2}-4X-3}}+{\frac {X^{2}-3}{3X^{2}+5}}.}$

3. Das Inverse von

   ${\displaystyle {\frac {6X^{3}-9X^{2}+5X-1}{X^{4}-4X^{3}+3X^{2}-8X-3}}.}$