Bài 2.

a,$\dfrac{5}{6}$ và $\dfrac{3}{4}$ 

$\dfrac{5}{6}$ = $\dfrac{5 × 4}{6 × 4}$ = $\dfrac{20}{24}$

$\dfrac{3}{4}$ = $\dfrac{3 × 6}{4 × 6}$ = $\dfrac{18}{24}$

Vậy $\dfrac{5}{6}$ > $\dfrac{3}{4}$

b,$\dfrac{7}{9}$ và $\dfrac{9}{11}$

$\dfrac{7}{9}$ = $\dfrac{7 × 11}{9 × 11}$ = $\dfrac{77}{99}$

$\dfrac{9}{11}$ = $\dfrac{9 × 9}{11 × 9}$ = $\dfrac{81}{99}$

Vậy $\dfrac{7}{9}$ < $\dfrac{9}{11}$

c,$\dfrac{4}{12}$ và $\dfrac{9}{15}$

$\dfrac{4}{12}$ = $\dfrac{4 × 15}{12 × 15}$ = $\dfrac{60}{180}$

$\dfrac{9}{15}$ = $\dfrac{9 × 12}{15 × 12}$ = $\dfrac{108}{180}$

Vậy $\dfrac{4}{12}$ < $\dfrac{9}{15}$ 

d,$\dfrac{45}{60}$ và $\dfrac{72}{96}$

$\dfrac{45}{60}$ = $\dfrac{45 × 96}{60 × 96}$ = $\dfrac{4320}{5760}$

$\dfrac{72}{96}$ = $\dfrac{72 × 60}{96 × 60}$ = $\dfrac{4320}{5760}$

$\dfrac{45}{60}$ = $\dfrac{72}{96}$

Bài 3

$\dfrac{11}{13}$ = $\dfrac{11 × 11}{13 × 11 }$ = $\dfrac{121}{143}$

$\dfrac{9}{11}$ = $\dfrac{9 × 13}{11 × 13}$ = $\dfrac{117}{143}$

 $#anhvu19120122#$
#$BTS$

`@Anh`

`2.`

`a)5/6` và `3/4`

`->15/18` > `15/20`

`b)7/9` và `9/11`

`->63/81` < `63/77`

`c)4/12` và `9/15`

`->36/108` < `36/60`

`d)45/60` và `72/96`

`->9/12` = `9/12`

`3.`

`11/13=(11xx11)/(13xx11)=121/143`

`9/11=(9xx13)/(11xx13)=117/143`

Mẫu số chung: 143