So sánh phân số:

a) \[\frac{3}{7}\] và \[\frac{5}{9}\]

Ta có: \[\frac{3}{7} = \frac{{3 \times 9}}{{7 \times 9}} = \frac{{27}}{{63}}\]

     \[\frac{5}{9} = \frac{{5 \times 7}}{{9 \times 7}} = \frac{{35}}{{63}}\]

Do đó: \[\frac{5}{9}\] > \[\frac{3}{7}\](\[\frac{{35}}{{63}}\] > \[\frac{{27}}{{63}}\])

b) \[\frac{6}{7}\] và \[\frac{7}{6}\]

Ta có: \[\frac{6}{7} = \frac{{6 \times 6}}{{7 \times 6}} = \frac{{36}}{{42}}\]

 \[\frac{7}{6} = \frac{{7 \times 7}}{{6 \times 7}} = \frac{{49}}{{42}}\]

Do đó: \[\frac{7}{6}\] > \[\frac{6}{7}\] (\[\frac{{49}}{{42}}\] > \[\frac{{36}}{{42}}\])

c) \[\frac{9}{{10}}\] và \[\frac{2}{{14}}\]

Ta có: \[\frac{9}{{10}} = \frac{{9 \times 7}}{{10 \times 7}} = \frac{{63}}{{70}}\]

 \[\frac{2}{{14}} = \frac{{2 \times 5}}{{14 \times 5}} = \frac{{10}}{{70}}\]

Do đó: \[\frac{9}{{10}}\] > \[\frac{2}{{14}}\] (\[\frac{{63}}{{70}}\] > \[\frac{{10}}{{70}}\])