1.
`39/42 = (39 : 3)/(42 : 3) = 13/14`
`1313/1414 =(1313 : 101)/1414:101 = 13/14`
`1313/1414 =(1313 : 101)/1414:101 = 13/14`
`⇒ 13/14 = 13/14 = 13/14` hay `39/42 = 1313/1414 = 1313/1414`
2.
`4/5 = (4.693)/5.693 = 2772/3465`
`8/7 = (8.495)/7.495 =3960/3465`
`8/9 = (8.385)/9.385 = 3080/3465`
`12/11 = (12.315)/11.315 = 3780/3465`
`⇒ 3960/3465 > 3780/3465 > 3080/3465 > 2772/3465` hay `8/7> 12/11 > 8/9> 4/5`
(Sai thì bảo nha )