Ta có: 18/46 = 18 x 45/46 x 45 = 810/2070 ; 21/45 = 21 x 46/45 x 46 = 966/2070

Nếu: 810/2070   <   966/2070

Vậy: 18/46     <     21/45

Hok tốt

k nha

a) \(1=\frac{45}{46}+\frac{1}{46}\)

    \(1=\frac{2011}{2012}+\frac{1}{2012}\)

Vì \(\frac{1}{46}>\frac{1}{2012}\)\(\Rightarrow\)\(\frac{45}{46}< \frac{2011}{2012}\)

b)Vì 2010/2011 < 1 và 17/16 > 1 => 2010/2011 < 17/16

a. 19/ 20= 1- 1/20

    20/ 21= 1- 1/21

mà 1/20> 1/21 => 19/ 20< 20/ 21

b. 17/ 21= 1- 4/21

    23/ 27= 1- 4/27

mà 4/21< 4/27 => 17/21< 23/27

c. 31/29= 1+ 2/29

    45/43= 1+ 2/43

mà 2/29> 2/43 => 31/29> 45/43

- Cho mình hỏi bài c là so sánh bằng cách gì ?

a: \(\frac{35}{40}=\frac{35:5}{40:5}=\frac78;\frac{105}{121}<\frac{105}{120}=\frac78\)

Do đó: \(\frac{105}{121}<\frac{35}{40}\)

b: \(\frac{18}{46}<\frac{18}{45}=\frac25;\frac{21}{45}>\frac{18}{45}=\frac25\)

Do đó: \(\frac{21}{45}>\frac{18}{46}\)

Ta có : 

        \(\frac{19}{21}>\frac{15}{21}\) (1)

         \(\frac{15}{21}>\frac{15}{23}\) (2)

Từ (1) và (2) => \(\frac{19}{21}>\frac{15}{23}\)

Ta có 

\(\frac{19}{21}\)\(>\frac{15}{21}\)( 1 )

 \(\frac{15}{21}>\frac{15}{23}\)( 2 )

Từ ( 1 ) và ( 2 ) suy ra \(\frac{19}{21}>\frac{15}{23}\)

\(\frac{43}{171}\)và \(\frac{45}{169}\)Phân số trung gian là: \(\frac{43}{169}\)

Ta thấy: \(\frac{43}{171}\)< \(\frac{43}{169}\)< \(\frac{45}{169}\)nên \(\frac{43}{171}\)< \(\frac{45}{169}\)

tk nhé

Ta có:\(\frac{43}{171}< \frac{43}{169}\)

Mà \(\frac{43}{169}< \frac{45}{169}\Rightarrow\frac{43}{171}< \frac{45}{169}\)

43/6>42/6=7>5

39/8<40/8=5

=>43/6>5>39/8

=>43/6>39/8

a: \(\frac{23}{35}<\frac{23,1}{35}=0,66\)

\(0,66=\frac{20,46}{31}<\frac{21}{31}\)

Do đó: \(\frac{23}{35}<\frac{21}{31}\)

b: \(\frac{-17}{24}<\frac{-16}{24}=\frac{-2}{3}\)

\(\frac{-2}{3}=\frac{-13}{19,5}<\frac{-13}{28}\)

Do đó: \(-\frac{17}{24}<-\frac{13}{28}\)

c: \(\frac{9}{16}>\frac{8}{16}=\frac12;\frac12=\frac{12}{24}>\frac{11}{24}\)

Do đó: \(\frac{9}{16}>\frac{11}{24}\)

\(\dfrac{58}{21}=2\dfrac{16}{21}=2+\dfrac{16}{21}=2+\left(1-\dfrac{5}{21}\right)=3-\dfrac{5}{21}\)

\(\dfrac{61}{22}=2\dfrac{17}{22}=2+\dfrac{17}{22}=2+\left(1-\dfrac{5}{22}\right)=3-\dfrac{5}{22}\)

Ta có

\(\dfrac{5}{21}>\dfrac{5}{22}\Rightarrow3-\dfrac{5}{21}< 3-\dfrac{5}{22}\Rightarrow\dfrac{58}{61}< \dfrac{61}{22}\)