Bài $2$.
$a$) Vì : `-1/5 < 0; 1/{1000} > 0`
`⇒ -1/5 < 0 < 1/1000`
`⇔ -1/5 < 1/1000`
$b$) Vì : `{267}/{268} < 1; {1347}/{1343} > 1`
`⇒ {267}/{268} < 1 < {1347}/{1343}`
`⇒ {267}/{268} < {1347}/{1343}`
$c$) Ta có: `-9/21 = {-3}/7`
`{27}/{-63} = {3}/-7`
Vì : `{-3}/7 = 3/{-7}` `⇒` `{-9}/21 = {27}/{-63}`
$d$) Ta có : $\dfrac{313131}{181818} = \dfrac{313131 : 10101}{181818 : 10101} = \dfrac{31}{18}$
$⇒ \dfrac{31}{18} = \dfrac{313131}{181818}$
Bài $3$.
$a$) `-12/15 + 4/26`
`= -4/5 + 2/13`
`= {-52+10}/65`
`= -42/65`
$b$) `-1/21 + {-1}/14`
`= {-2-3}/42`
`= {-5}/42`
$c$) `-1/9 - 5/12`
`= {-4-15}/36`
`= -19/36`
$d$) `5/8 - 7/10`
`= {25-28}/40`
`= -3/40`
