Bài `1` : Dưới hình

Bài `2` : 

Ta có : `13/38>0`

          : `0>{-12}/{-37}`

`⇒13/38>0>{-12}/{-37}`

`⇒13/38>{-12}/{-37}`

Bài `3` : 

`a,` `1/3 . 4/5+1/3 . 6/5`

`=1/3(4/5+6/5)`

`=1/3 . 10/5`

`=1/3 . 2`

`=2/3`

`b,` `3/7 . 9/26-1/26 . 9/7`

`=3/26 . 9/7-1/26 . 9/7`

`=9/7(3/26-1/26)`

`=9/7 . 1/13`

`=9/91`

`c,` $\dfrac{155-\dfrac{10}{7}-\dfrac{5}{11}+\dfrac{5}{23}}{403-\dfrac{26}{7}-\dfrac{13}{11}+\dfrac{13}{23}}$

$=\dfrac{5.31-\dfrac{5}{3,5}-\dfrac{5}{11}+\dfrac{5}{23}}{13.31-\dfrac{13}{3,5}-\dfrac{13}{11}+\dfrac{13}{23}}$

$=\dfrac{5\left(31-\dfrac{1}{3,5}-\dfrac{1}{11}+\dfrac{1}{23}\right)}{13\left(31-\dfrac{1}{3,5}-\dfrac{1}{11}+\dfrac{1}{23}\right)}$

`=5/13`