+ Ta có:

17/15 > 1; 29/30 < 1

=> 17/15 > 29/30

+ Ta có:

12/48 < 12/47 < 13/47

=> 12/48 < 13/47

+ 15/22 = 60/88 > 60/91

=> 15/22 > 60/91

(-25)-(-12)= - 13

18+(14-42)=18+(-28) = -10

(-18)-13+17=(-31) +17= -14

\(\rightarrow\)-13 < -10 > -14\(\Rightarrow\) (-25)-(-12) < 18+(14-42) > (-18)-13+17

a) Ta có:

\(\frac{23}{3}=\frac{21+2}{3}=\frac{21}{3}+\frac{2}{3}=7+\frac{2}{3}\)

\(\frac{15}{2}=\frac{14+1}{2}=\frac{14}{2}+\frac{1}{2}=7+\frac{1}{2}\)

Lại có:\(1-\frac{2}{3}=\frac{1}{3}< 1-\frac{1}{2}=\frac{1}{2}\Rightarrow\frac{2}{3}>\frac{1}{2}\)

\(\Rightarrow\frac{23}{3}>\frac{15}{2}\)

a, 23/3 và 15/2

Ta có : 

23/3 = 23x2/3x2 = 46/6.                                      15/2 = 15x3/2x3 = 45/6.

Vậy 46/6 > 45/6 nên 23/3 > 15/2.

b, 4/17 và 2/9.

Ta có :

4/17 = 4x9/17x9 = 36/153.                                   2/9 = 2x17/9x17 = 34/153.

Vậy 36/153 > 34/153 nên 4/17 > 2/9.

Ta có:\(\frac{12}{17}>\frac{12}{24}=\frac{1}{2}\)(1)

\(\frac{7}{15}< \frac{7}{14}=\frac{1}{2}\)(2)

Từ (1) và (2) suy ra:\(\frac{12}{17}>\frac{7}{15}\)

\(\dfrac{-14}{21};\dfrac{-2}{15};\dfrac{14}{-35}\)

\(\dfrac{-17}{21}=\dfrac{-85}{105}\);\(\dfrac{-2}{15}=\dfrac{-14}{105};\dfrac{14}{-35}=\dfrac{-14}{35}=\dfrac{-42}{105}\)

\(\dfrac{17}{60};\dfrac{5}{12};\dfrac{64}{90}\)

\(\dfrac{17}{60}=\dfrac{51}{180};\dfrac{-5}{12}=\dfrac{-75}{180};\dfrac{-64}{90}=\dfrac{-32}{45}=\dfrac{-128}{180}\)

bài2:

a)\(\dfrac{3}{5}>\dfrac{4}{7}\)

b)\(\dfrac{-5}{8}< \dfrac{-7}{12}\)

c)\(\dfrac{5}{-3}< \dfrac{-9}{12}\)

a,3/4<4/5

b,7/12>17/36

c,5/6 <6/7 < 7/8

giai thich nua nhe cac bn

a, Ta có : 1 - 3/4 = 1/4 ; 1 - 4/5 = 1/5 

Vì 1/4 > 1/5 nên 3/4 < 4/5

b, Ta có :7/12 = 21/36

Vì 21/36 > 17/36 nên 7/12 > 17/36

c, Ta có:

1 - 5/6 = 1/6

1 - 6/7 = 1/7

1 - 7/8 = 1/8

Vì 1/6 > 1/7 > 1/8 nên 5/6 < 6/7 < 7/8

a) 3/4 < 1

115/14 > 1 

=> 3/4 < 115/14

b) 2000/1999 > 1

1998/1999 < 1

=> 2000/1999>1998/1999

c)-17/234 < 0 , 1/1995 > 0

=> -17/234 < 1/1995

d) 23/-15 < 0 ; -17/-49>0

=> 23/-15 < -17/-49