chắc thế này :
\(\frac{9}{17}.\frac{21}{13}+\frac{5}{17}.\frac{9}{13}-\frac{8}{17}.2\)
\(=\frac{9}{17}.\frac{21}{13}+\frac{5}{13}.\frac{9}{17}-\frac{8}{17}.2\)
\(=\frac{9}{17}.\left(\frac{21}{13}+\frac{5}{13}\right)-\frac{8}{17}.2\)
\(=\frac{9}{17}.2-\frac{8}{17}.2\)
\(=2.\left(\frac{9}{17}-\frac{8}{17}\right)\)
\(=2.\frac{1}{17}\)
\(=\frac{2}{17}\)
1/17.(189/13+45/13)-16/17=1/17.18-16/17=18/17-16/17=2/17