1. Выполните сложение: a) -64 + 79; б) 49 + (-52); в) -3,75 + 0,785; г) -2/7 + 5/42; д) 3/4 + (-11/21); ж) -4/9 + 1;

a) $$-64 + 79 = 15$$ б) $$49 + (-52) = 49 - 52 = -3$$ в) $$-3,75 + 0,785 = -2,965$$ г) $$-\frac{2}{7} + \frac{5}{42} = -\frac{2 \cdot 6}{7 \cdot 6} + \frac{5}{42} = -\frac{12}{42} + \frac{5}{42} = \frac{-12 + 5}{42} = \frac{-7}{42} = -\frac{1}{6}$$ д) $$\frac{3}{4} + \left(-\frac{11}{21}\right) = \frac{3}{4} - \frac{11}{21} = \frac{3 \cdot 21}{4 \cdot 21} - \frac{11 \cdot 4}{21 \cdot 4} = \frac{63}{84} - \frac{44}{84} = \frac{63 - 44}{84} = \frac{19}{84}$$ ж) $$-\frac{4}{9} + 1 = -\frac{4}{9} + \frac{9}{9} = \frac{-4 + 9}{9} = \frac{5}{9}$$