Ответ:

[tex]1)9 \frac{1}{18} [/tex]

[tex]2) - 4 \frac{25}{36} [/tex]

[tex]3) \frac{163}{42} [/tex]

Пошаговое объяснение:

[tex]1)6 \frac{2}{9} + (2 \frac{ 5}{6} ) = (6 + 2) + ( \frac{2}{9} + \frac{5}{6} ) = 8 + \frac{2}{9} + \frac{5}{6} ) = 8 + \frac{19}{18} = 8 + 1 \frac{1}{18} = 8 + 1 + \frac{1}{18} = 9 + \frac{1}{18} = 9 \frac{1}{18} [/tex]

[tex]2) - 1 \frac{7}{9} + ( - 2 \frac{11}{12} ) = - 1 \frac{7}{9} - 2 \frac{11}{12} = - (1 \frac{7}{9} + 2 \frac{11}{12} ) = - ((1 + 2) + ( \frac{7}{9} + \frac{11}{12} )) = - ( 3 + ( \frac{7}{9} + \frac{11}{12} )) = - (3 + \frac{61}{36} ) = - (3 + 1 \frac{25}{36} ) = - (3 + 1 + \frac{25}{36} ) = - (4 + \frac{25}{36} = - 4 \frac{25}{36} [/tex]

[tex]6 \frac{1}{6} + ( - 2 \frac{2}{7} ) = \frac{37}{6} + ( - 2 \frac{2}{7} ) = \frac{37}{6} - 2 \frac{2}{7} = \frac{37}{6} - \frac{16}{7} = = \frac{163}{42} [/tex]