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a) Ta có: \(\frac{13}{21}=\frac{26}{42}\)

\(\frac{9}{14}=\frac{27}{42}\)

\(\frac{26}{42}< \frac{27}{42}\) nên \(\frac{13}{21}< \frac{9}{14}\)

b) Ta có: \(\frac{7}{-12}=\frac{-21}{36}\)

\(\frac{11}{-18}=\frac{-22}{36}\)

\(\frac{-21}{36}>\frac{-22}{36}\) nên \(\frac{7}{-12}>\frac{11}{-18}\)

c) Ta có: \(\frac{17}{58}=\frac{510}{1740}\)

\(\frac{13}{60}=\frac{377}{1740}\)

\(\frac{510}{1740}>\frac{377}{1740}\) nên \(\frac{17}{58}>\frac{13}{60}\)

d) Ta có: \(\frac{-19}{33}=\frac{-703}{1221}\)

\(\frac{-17}{37}=\frac{-561}{1221}\)

\(\frac{-703}{1221}< \frac{-561}{1221}\) nên \(\frac{-19}{33}< \frac{-17}{33}\)

e) Ta có: \(\frac{67}{77}=\frac{5561}{6391}\)

\(\frac{73}{83}=\frac{5621}{6391}\)

\(\frac{5561}{6391}< \frac{5621}{6391}\) nên \(\frac{67}{77}< \frac{73}{83}\)

f) Ta có: \(\frac{-456}{461}=\frac{-58368}{59008}\)

\(\frac{-123}{128}=\frac{-56703}{59008}\)

\(\frac{-58368}{59008}< \frac{-56703}{59008}\) nên \(\frac{-456}{461}< \frac{-123}{128}\)

4 tháng 7 2017

Bài 1 : 

1) Ta có : \(\frac{19}{18}=1+\frac{1}{18}\)

               \(\frac{2019}{2018}=1+\frac{1}{2018}\)

Vì \(\frac{1}{18}>\frac{1}{2018}\)

Nên : \(\frac{19}{18}>\frac{2019}{2018}\)

15 tháng 8 2020

a) 12 < 13; 49 > 47 => 12/49 < 13/47

b) 64 < 73; 85 > 81 => 64/85 < 73/81

c) 19 > 17; 31 < 35 => 19/31 > 17/35

d) 67/77 = 1 - 10/77; 73/83 = 1- 10/83. Mà 10/77 > 10/83 => 67/77 < 73/83.

e) 456/461 = 1 - 5/461; 123/128 = 1 - 5/128. Mà 5/461 < 5/128 => 456/461 > 123/128.

f) 149/157 = 1 - 8/157; 449/458 = 1 - 9/458. Mà 8/157 = 16/314 > 9/458 => 149/157 < 449/458.

3 tháng 7 2017

a)\(12< 13;49>47\)

\(\Rightarrow\dfrac{12}{49}< \dfrac{13}{47}\)

b)\(\dfrac{64}{85}>\dfrac{43}{85}\Rightarrow\dfrac{64}{85}>\dfrac{1}{2}\)

\(\dfrac{17}{35}< \dfrac{17}{34}\Rightarrow\dfrac{17}{35}< \dfrac{1}{2}\)

\(\Rightarrow\dfrac{17}{35}< \dfrac{64}{85}\)

c) \(\dfrac{19}{31}>\dfrac{16}{31}\Rightarrow\dfrac{19}{31}>\dfrac{1}{2}\)

\(\dfrac{17}{35}< \dfrac{17}{34}\Rightarrow\dfrac{17}{35}< \dfrac{1}{2}\)

\(\Rightarrow\dfrac{17}{35}< \dfrac{19}{31}\)

d)

\(1-\dfrac{67}{77}=\dfrac{10}{77}\)

\(1-\dfrac{73}{83}=\dfrac{10}{83}\)

\(\dfrac{10}{77}>\dfrac{10}{83}\Rightarrow\dfrac{67}{77}< \dfrac{73}{83}\)

e)\(1-\dfrac{456}{461}=\dfrac{5}{461}\)

\(1-\dfrac{123}{128}=\dfrac{5}{128}\)

\(\dfrac{5}{461}< \dfrac{5}{128}\Rightarrow\dfrac{456}{461}>\dfrac{123}{128}\)

3 tháng 7 2017

\(a,\dfrac{12}{49}< \dfrac{12}{47}< \dfrac{13}{47}\Rightarrow\dfrac{12}{49}< \dfrac{12}{47}\)

b, Ta có: \(\dfrac{17}{35}=\dfrac{51}{105}\)

\(\dfrac{64}{85}>\dfrac{64}{105}>\dfrac{51}{105}\Rightarrow\dfrac{64}{85}>\dfrac{51}{105}\) hay \(\dfrac{64}{85}>\dfrac{17}{85}\)

c,\(\dfrac{19}{31}>\dfrac{17}{31}>\dfrac{17}{35}\Rightarrow\dfrac{19}{31}>\dfrac{17}{35}\)

d, \(\dfrac{67}{77}+\dfrac{10}{77}=1\)

\(\dfrac{73}{83}+\dfrac{10}{83}=1\)

\(\dfrac{10}{77}>\dfrac{10}{83}\Rightarrow\dfrac{67}{77}< \dfrac{73}{83}\)

e, \(\dfrac{456}{461}+\dfrac{5}{461}=1\)

\(\dfrac{123}{128}+\dfrac{5}{128}=1\)

\(\dfrac{5}{461}< \dfrac{5}{128}\Rightarrow\dfrac{456}{461}>\dfrac{123}{128}\)

19 tháng 2 2017

                              12/49  >   13/47

                                64/85   >  73/81

                                19/31    > 17/35 

                                 67/77   >  73/83