Question

So sánh các phân số:

a) \(\dfrac{3}{7}\) và \(\dfrac{2}{5}\);                b) \(\dfrac{5}{9}\) và \(\dfrac{5}{8}\);                c) \(\dfrac{8}{7}\) và \(\dfrac{7}{8}\).

Answer 1

Answer 2

`3/7-2/5`

`=1/35>0`

`=>3/7>2/5`

`b,9>8`

`=>1/9<1/8`

`=>5/9<5/8`

`d,8/7>1`

`7/8<1`

`=>8/7>7/8`

Answer 3

a) Ta có: \(\dfrac{3}{7}=\dfrac{15}{35}\)

\(\dfrac{2}{5}=\dfrac{14}{35}\)

Do đó: \(\dfrac{3}{7}>\dfrac{2}{5}\)

b) Ta có: 9>8

nên \(\dfrac{5}{9}< \dfrac{5}{8}\)

c) Ta có: \(\dfrac{8}{7}>1\)

\(1>\dfrac{7}{8}\)

Do đó: \(\dfrac{8}{7}>\dfrac{7}{8}\)

Answer 4

\(\dfrac{3}{7}=\dfrac{3.5}{7.5}=\dfrac{15}{35}\)

\(\dfrac{2}{5}=\dfrac{2.7}{5.7}=\dfrac{14}{35}\)

\(\dfrac{15}{35}>\dfrac{14}{35}\) \(\rightarrow\dfrac{3}{7}>\dfrac{2}{5}\)

\(\dfrac{5}{9}< \dfrac{5}{8}\)

\(\dfrac{8}{7}=\dfrac{8.8}{7.8}=\dfrac{64}{56}\)

\(\dfrac{7}{8}=\dfrac{7.7}{8.7}=\dfrac{49}{56}\)

\(\dfrac{64}{56}>\dfrac{49}{56}\rightarrow\dfrac{8}{7}>\dfrac{7}{8}\)