Дам 30 баллов за решение

Решите задачу:

$1)\;5^8\cdot2^6:10^7=5^8\cdot2^6:(5^7\cdot2^7)=5^{8-7}\cdot2^{6-7}=5^1\cdot2^{-1}=\frac52=2\frac12\\2)\;\frac{\sqrt[3]3\cdot\sqrt[4]{4}}{\sqrt[12]3}=3^{\frac13}\cdot4^{\frac14}\cdot3^{-\frac1{12}}=3^{\frac13-\frac1{12}}\cdot4^{\frac14}=3^{\frac14}\cdot4^{\frac14}=12^{\frac14}=\sqrt[4]{12}\\3)\;\frac{x^5\cdot x^6}{x^9}=x^{5+6-9}=x^2=(12)^2=144\\4)\;f(y)=(2y-\frac3y)(3y-\frac2y)=6y^2+\frac6{y^2}-13\\f(\frac1y)=6\cdot\frac1{y^2}+\frac6{\frac1{y^2}}-13=\frac6{y^2}+6y^2-13\\\frac{f(y)}{f(\frac1y)}=1$
$5)\;\sin^235^o+\sin^2125^o=\frac{1-\cos70^o}2+\frac{1-\cos250^o}2=\frac{2-(\cos70^o+\cos250^o)}2=\\=\frac{2-2\cos160^o\cos90^o}2=\frac{2-0}2=1\\\frac8{\sin^235^o+\sin^2125^o}=\frac81=8\\6)\;4\cos2\alpha=4\cdot(2\cos^2\alpha-1)=4\cdot(2\cdot\frac1{16}-1)=4\cdot(\frac18-1)=\\=4\cdot(-\frac78)=-\frac74=-1\frac34$