7*. Вычислите: a) \(\frac{\frac{1}{2} - \frac{1}{7} - \frac{1}{4}}{2 \frac{5}{14} - 1 \frac{8}{21} - \frac{1}{3}}\); б) \(\frac{-7 \cdot 1 \frac{3}{7} : (-1 \frac{2}{3})}{-2,52 : (-8,4)}\)

7*. Вычислите: a) \(\frac{\frac{1}{2} - \frac{1}{7} - \frac{1}{4}}{2 \frac{5}{14} - 1 \frac{8}{21} - \frac{1}{3}} = \frac{\frac{14 - 4 - 7}{28}}{\frac{33}{14} - \frac{29}{21} - \frac{1}{3}} = \frac{\frac{3}{28}}{\frac{99 - 58 - 14}{42}} = \frac{\frac{3}{28}}{\frac{27}{42}} = \frac{3}{28} \cdot \frac{42}{27} = \frac{3 \cdot 42}{28 \cdot 27} = \frac{3 \cdot 3 \cdot 14}{14 \cdot 2 \cdot 3 \cdot 9} = \frac{1}{2} \cdot \frac{1}{3} = \frac{1}{6}\) б) \(\frac{-7 \cdot 1 \frac{3}{7} : (-1 \frac{2}{3})}{-2,52 : (-8,4)} = \frac{-7 \cdot \frac{10}{7} : (-\frac{5}{3})}{-2,52 : (-8,4)} = \frac{-10 : (-\frac{5}{3})}{-2,52 : (-8,4)} = \frac{-10 \cdot (-\frac{3}{5})}{0,3} = \frac{6}{0,3} = 20\)