1. \(\frac{7}{39}=\frac{140}{780};\frac{11}{65}=\frac{132}{780};\frac{9}{52}=\frac{135}{780}\) và thứ tự tăng dần là : \(\frac{132}{780}< \frac{135}{780}< \frac{140}{780}\)

2. \(\frac{17}{20}=\frac{153}{180};-\frac{19}{30}=-\frac{114}{180};\frac{38}{45}=\frac{152}{180};-\frac{13}{10}=-\frac{130}{180}\) và thứ tự tăng dận là : 

\(-\frac{130}{180}< -\frac{114}{180}< \frac{152}{180}< \frac{153}{180}\)

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3/5=36/60;3/4=45/60;7/12=35/60

35/60<36/60<45/60 nên 7/12<3/5<3/4

Bài 1: 

a: 3/4=54/72

-1/9=-8/72

-5/8=-45/72

b: -1/7=-8/56

-1/-8=1/8=7/56

3/4=42/56

3/2,5/5,2/3,3/5,3/4,2/5

\(\dfrac{9}{382};\dfrac{6}{257};\dfrac{15}{643}\)

\(BCNN\left(9,6,15\right)=90.\)

\(\Rightarrow\) Ta có:

\(\dfrac{9}{382}=\dfrac{9\times10}{382\times10}=\dfrac{90}{3820}.\)

\(\dfrac{6}{257}=\dfrac{6\times15}{257\times15}=\dfrac{90}{3855}.\)

\(\dfrac{15}{643}=\dfrac{15\times6}{643\times6}=\dfrac{90}{3858}.\)

Mà \(\dfrac{90}{3820}>\dfrac{90}{3855}>\dfrac{90}{3858}\). Do đó \(\dfrac{9}{382}>\dfrac{6}{257}>\dfrac{15}{643.}\)

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Ta có:

\(\frac{{ - 2}}{5} = \frac{{ - 2.8}}{{5.8}} = \frac{{ - 16}}{{40}}\)

\(\frac{{ - 3}}{8} = \frac{{ - 3.5}}{{8.5}} = \frac{{ - 15}}{{40}}\)

\(\frac{3}{{ - 4}} = \frac{{ - 3}}{4} = \frac{{ - 3.10}}{{4.10}} = \frac{{ - 30}}{{40}}\)

Do -30 < -16 < -15 nên \(\frac{{ - 30}}{{40}} < \frac{{ - 16}}{{40}} < \frac{{ - 15}}{{40}}\). Do đó \(\frac{3}{{ - 4}} < \frac{{ - 2}}{5} < \frac{{ - 3}}{8}\).

\(\dfrac{3}{5}=\dfrac{36}{60};\dfrac{3}{4}=\dfrac{45}{60};\dfrac{7}{12}=\dfrac{35}{60}\\ \dfrac{35}{60}< \dfrac{36}{60}< \dfrac{45}{60}\Rightarrow\dfrac{7}{12}< \dfrac{3}{5}< \dfrac{3}{4}\)

5/9= 15/27 > 1/2

12/25 < 1/2

2/5 = 10/25 < 12/25

14/27 < 15/27 

vậy: 10/25< 12/25 < 14/27 < 15/27

Nên: 2/5 < 12/25 < 14/27 < 5/9