\(a)\,{25^3}:{5^2} = {25^3}:25 = {25^2} = 625\)
\(\displaystyle b)\,{\left( {{3 \over 7}} \right)^{21}}:{\left( {{9 \over {49}}} \right)^6}\)
\(\displaystyle = {\left( {{3 \over 7}} \right)^{21}}:{\left[ {{{\left( {{3 \over 7}} \right)}^2}} \right]^6} \)
\(\displaystyle = {\left( {{3 \over 7}} \right)^{21}}:{\left( {{3 \over 7}} \right)^{12}} \)
\(\displaystyle = {\left( {{3 \over 7}} \right)^9} = {{19683} \over {40353607}}\)
\(c) \,\displaystyle3 - {\left( { - {6 \over 7}} \right)^0} + {\left( {{1 \over 2}} \right)^2}:2\)
\(\displaystyle= 3 - 1 + {\left( {{1 \over 2}} \right)^2}.\frac{1}{2}\)
\(\displaystyle = 2 + {1 \over 8} = 2{1 \over 8}\)
