выполните сложение: а) -\frac{7}{24} + \frac{5}{18}; е) \frac{5}{42} + (-\frac{11}{63}); ж)-1+\frac{4}{9}; з) 1\frac{9}{20} + ( -1\frac{8}{15}).

Ответ:

1. -\frac{7}{24} + \frac{5}{18} = -\frac{7\cdot3}{24\cdot3} + \frac{5\cdot4}{18\cdot4} = -\frac{21}{72} + \frac{20}{72} = -\frac{1}{72}
2. \frac{5}{42} + (-\frac{11}{63}) = \frac{5\cdot3}{42\cdot3} - \frac{11\cdot2}{63\cdot2} = \frac{15}{126} - \frac{22}{126} = -\frac{7}{126} = -\frac{1}{18}
3. -1+\frac{4}{9} = -\frac{9}{9} + \frac{4}{9} = -\frac{5}{9}
4. 1\frac{9}{20} + ( -1\frac{8}{15}) = \frac{29}{20} - \frac{23}{15} = \frac{29\cdot3}{20\cdot3} - \frac{23\cdot4}{15\cdot4} = \frac{87}{60} - \frac{92}{60} = -\frac{5}{60} = -\frac{1}{12}

Ответ: -1/72; -1/18; -5/9; -1/12