`5/21 ; (-3)/28` `và` `(-45)/108`
`-> 5/21 ; (-3)/28 ; (-45)/108 = (-5)/12`
`-> 12 = 2^2 . 3`
`21 = 3 . 7`
`28 = 2^2 . 7`
`ƯCLN ( 12 , 28 ) = 2^2 . 3 . 7 = 84`
`84 : 12 = 7`
`84 : 28 = 3`
`84 : 21 = 4`
Quy đồng :
`5/21 = 5.4/21.4 = 20/84`
`(-3)/28 = ((-3).3)/28.3 = (-9)/84`
`(-5)/12 = ((-5) . 7) / (12 . 7) = (-35)/84`