So sánh phân số mà không quy đồng mẫu số:

Đảo ngược phân số để so sánh

a) $\frac{2008}{2009}$ = $\frac{2009}{2008}$

Mà: $\frac{2007}{2008}$ < $\frac{2009}{2008}$ 

=> $\frac{2007}{2008}$ < $\frac{2008}{2009}$ 

b) $\frac{3}{4}$ = $\frac{4}{3}$ 

Mà: $\frac{2}{3}$ < $\frac{4}{3}$

=>  $\frac{2}{3}$ < $\frac{3}{4}$ 

c) $\frac{2}{13}$ = 1- $\frac{11}{13}$

$\frac{3}{14}$ = 1 - $\frac{11}{14}$

Mà: $\frac{1}{13}$ > $\frac{1}{14}$

=> $\frac{2}{13}$ < $\frac{3}{14}$

d)$\frac{5}{14}$ = 1- $\frac{9}{14}$

$\frac{2}{11}$ = 1 - $\frac{9}{11}$

Mà: $\frac{9}{14}$ < $\frac{9}{11}$

=> $\frac{5}{14}$ > $\frac{2}{11}$

e)$\frac{5}{6}$ = 1- $\frac{1}{6}$

$\frac{9}{10}$ = 1 - $\frac{1}{10}$

Mà: $\frac{1}{6}$ > $\frac{1}{10}$

=> $\frac{5}{6}$ < $\frac{9}{10}$

f)$\frac{77}{78}$ = 1- $\frac{1}{78}$

$\frac{78}{79}$ = 1 - $\frac{1}{79}$

Mà: $\frac{1}{78}$ > $\frac{1}{79}$

=> $\frac{77}{78}$ < $\frac{78}{79}$

CHO MIK XIN CTLHN NHA

`a ) 2007/2008 = 1 - 1/2008`

`2008/2009 = 1 - 1/2009`

`1/2008 > 1/2009 => 2007/2008 < 2008/2009`

`b ) 2/3 = 1 - 1/3`

`3/4 = 1 - 1/4`

`1/3 > 1/4 => 2/3 < 3/4`

`c ) 2/13 = 1 - 11/13`

`3/14 = 1 - 11/14`

`11/13 > 11/14 => 2/13 < 3/14`

`d ) 5/14 = 1 - 9/14`

`2/11 = 1 - 9/11`

`9/14 < 9/11 => 5/14 > 2/11`

`e ) 5/6 = 1 - 1/6`

`9/10 = 1 - 1/10`

`1/6 > 1/10 => 5/6 < 9/10`

`f ) 77/78 = 1 - 1/78`

`78/79 = 1 - 1/79`

`1/78 > 1/79 => 77/78 < 78/79`

`#dtkc`