Vì `ƯCLN(a,b)=4`
`=>a=4m,b=4n`
`(ƯCLN(m,n)=1,m,n∈N)`
`=>a.b=4m.4n=448`
`=>16mn=448`
`=>mn=448:16=28`
Vì `a<b=>4m<4n=> m<n`
Ta có: `m<n,ƯCLN(m,n)=1,mn=28`
`=>m=1;n=28` hoặc `m=4;n=7`
*Với `m=1;n=28` ta có:
`a=4m=4.1=4`
`b=4n=4.28=112`
*Với `m=4;n=7` ta có:
`a=4m=4.4=16`
`b=4n=4.7=28`
Vậy `a=4;b=112` hoặc `a=16;b=28`