Mathematrix: Aufgabenbeispiele/ Doppelbrüche

$\frac{\frac{2}{3}-\frac{3}{4}}{\frac{3}{5}-\frac{3}{4}}$ $=\frac{\frac{2}{3}\underset{\_}{\xcancel{-}}\frac{3}{4}}{\frac{3}{5}\underset{\_}{\xcancel{-}}\frac{3}{4}}=\frac{\frac{2\cdot 4-3\cdot 3}{3\cdot 4}}{\frac{3\cdot 4-5\cdot 3}{5\cdot 4}}=\frac{\frac{-1}{12}}{\frac{-3}{20}}=\frac{-1}{12}:\frac{-3}{20}=\frac{-1}{{\xcancel{12}}^3}\cdot \frac{{\xcancel{20}}^5}{-3}=\frac{5}{9}$