\(\begin{array}{l}a){( - 3)^8} = {( - 3)^7}.( - 3) = - 2187.( - 3) = 6561\\b){\left( { - \frac{2}{3}} \right)^{12}} = {\left( { - \frac{2}{3}} \right)^{11}}.\left( { - \frac{2}{3}} \right) = \frac{{ - 2048}}{{177147}}.\frac{{ - 2}}{3} = \frac{{4096}}{{531441}}\end{array}\)