\(\frac{4}{3}\times\frac{9}{8}\times...\times\frac{81}{80}=\frac{2^2}{1\times3}\times\frac{3^2}{2\times4}\times...\times\frac{9^2}{8\times10}\)
\(=\frac{2\times3\times4\times...\times9}{1\times2\times3\times...\times8}\times\frac{2\times3\times4\times...\times9}{3\times4\times5\times...\times10}\\ =\frac{9}{1}\times\frac{2}{10}=\frac{9}{5}\)
4/3.9/8.16/15.25/24.36/35.49/48.64/63.81/80
=3/2.16/15.25/24.36/35.49/48.64/63.81/80
=5/3.36/35.49/48.64/63.81/80
=7/4.64/63.81/80
=9/5
+