а)

[tex] \frac{5}{9} + ( - \frac{7}{9} ) = \frac{5}{9} - \frac{7}{9} = \frac{5 -7 }{9} = - \frac{2}{9} [/tex]

b)

[tex] \frac{ - 10}{19} + \frac{5}{19} = - \frac{10}{19} + \frac{5}{19} = \frac{5 - 10}{19} = - \frac{5}{19} [/tex]

c)

[tex] \frac{ - 12}{23} + ( \frac{ - 11}{23} ) = - \frac{12}{23} - \frac{11}{23} = \frac{ - 12 - 11}{23} = - \frac{23}{23} = - 1[/tex]

d)

[tex] \frac{16}{37} + \frac{11}{37} = \frac{16 + 11}{37} = \frac{27}{37} [/tex]