[tex]a^{-16}*\frac{a^{6}}{a^{-5}} =\frac{a^{6}*a^{5}}{a^{16}} =\frac{a^{6+5}}{a^{16}} =\frac{a^{11}}{a^{16}} =a^{11-16}=a^{-5}=\frac{1}{a^{5}}[/tex]