a) \(\dfrac{3}{4}=\dfrac{3\times4}{4\times4}=\dfrac{12}{16}\)

b) \(\dfrac{1}{3}=\dfrac{1\times3}{3\times3}=\dfrac{3}{9}\)

c) \(\dfrac{5}{6}=\dfrac{5\times3}{6\times3}=\dfrac{15}{18}\)

a) \(\dfrac{2}{5}=\dfrac{4}{10}\)

\(\dfrac{4}{10}>\dfrac{3}{10}\)

b) \(\dfrac{5}{6}=\dfrac{10}{12}\)

\(\dfrac{7}{12}< \dfrac{10}{12}\)

c) \(\dfrac{1}{2}=\dfrac{2}{4}\)

\(\dfrac{3}{4}< \dfrac{2}{4}\)

d) \(\dfrac{8}{3}=\dfrac{56}{21}\)

\(\dfrac{56}{21}>\dfrac{11}{21}\)

a)

 \(\dfrac{5}{9}< \dfrac{9}{9}\)

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

\(\dfrac{9}{9}=1\)

\(\dfrac{18}{4}>\dfrac{3}{4}\)

b) 

\(\dfrac{2}{5},\dfrac{3}{5},\dfrac{8}{5}\)

\(\dfrac{5}{2}=\dfrac{15}{6},\dfrac{1}{6},1=\dfrac{6}{6}\rightarrow\dfrac{1}{6},\dfrac{6}{6},\dfrac{15}{6}\)

Quy tắc:

Trong hai phân số có cùng mẫu, phân số nào có tử lớn hơn thì lớn hơn.

So sánh:

Ta có 7 < 9 nên \(\dfrac{7}{{11}} < \dfrac{9}{{11}}\).

a: 31/32>0>-5/57

b: -15/81<0<7/90

3/

a/ \(\dfrac{31}{32}>0>\dfrac{-5}{57}\)

b/ \(\dfrac{-15}{81}< 0< \dfrac{7}{90}\)

\(\dfrac{31}{32}>0>\dfrac{-5}{57}\)

a) \(\dfrac{6}{14}=\dfrac{6:2}{14:2}=\dfrac{3}{7}\)

\(\dfrac{3}{7}< \dfrac{4}{7}\)

b) \(\dfrac{6}{15}=\dfrac{6:3}{15:3}=\dfrac{2}{5}\)

\(\dfrac{3}{5}>\dfrac{2}{5}\)

c) \(\dfrac{10}{18}=\dfrac{10:2}{18:2}=\dfrac{5}{9}\)

\(\dfrac{5}{9}>\dfrac{2}{9}\)

-5/8=-35/56

-6/7=-48/56

mà -35>-48

nên -5/8>-6/7

\(\dfrac{-5}{8}và\dfrac{6}{-7}=\dfrac{-5}{8}và\dfrac{-6}{7}=\dfrac{-35}{56}và\dfrac{-48}{56}=>\dfrac{-35}{56}>\dfrac{-48}{56}hay\dfrac{-5}{8}>\dfrac{6}{-7}\)

-5/8=-45/56

6/-7=-48/56

->-5/8>6/-7