а) \(\frac{2^{12}-2^9}{7\cdot2^8}=\frac{2^9(2^3-1)}{7\cdot2^8}=\frac{2\cdot7}{7}=2\).
б) \(\frac{2\cdot5^{10}-5^{11}}{6\cdot5^{11}}=\frac{5^{10}(2-5)}{6\cdot5^{11}}=-\frac{3}{6\cdot5}=-\frac{1}{10}\).
в) \(\frac{3^{12}+3^{10}}{3^8}=\frac{3^{10}(3^2+1)}{3^8}=3^2\cdot10=90\).
г) \(\frac{5^8+5^6}{2\cdot5^7}=\frac{5^6(5^2+1)}{2\cdot5^7}=\frac{26}{2\cdot5}=\frac{13}{5}\).
Ответ: а) 2; б) \(-\frac{1}{10}\); в) 90; г) \(\frac{13}{5}\).