Thực hiện phép tính:

 a)\[ = \frac{5}{7} + \frac{{ - 1}}{2}\]

 \[ = \frac{{10}}{{14}} + \frac{{ - 7}}{{14}}\]

 \[ = \frac{3}{{14}}\]

 b)\( = \frac{1}{8}\,\,.\,\,\left( {\frac{{ - 5}}{3} + \frac{{ - 7}}{3}} \right)\)

 \( = \frac{1}{8}\,\,.\,\,\frac{{ - 12}}{3}\)

 \( = \frac{{ - 1}}{2}\).

 c) \( = \frac{{{3^{17}}\,.\,{{\left( {{3^4}} \right)}^{11}}}}{{{{\left( {{3^3}} \right)}^{10}}\,\,.\,\,{{\left( {{3^2}} \right)}^{15}}}}\)

 \[ = \frac{{{3^{17}}\,.\,{3^{44}}}}{{{3^{30}}\,\,.\,\,{3^{30}}}}\]

 \[ = \frac{{{3^{61}}}}{{{3^{60}}}} = 3\]