[tex] a)\frac{8}{7} - \frac{9}{7} + \frac{1}{7} = \\ \\ = \frac{8-9+1}{7} \\ \\ = \frac{0}{7} \\ \\ =0 \\ \\ b) \frac{1}{2} + \frac{1}{4} + \frac{1}{8} + \frac{1}{16} = \\ \\=\frac{8}{16} + \frac{4}{16} + \frac{2}{16} + \frac{1}{16} = \frac{8+4+2+1}{16} \\ \\ = \frac{15}{16} [/tex]