`a)` Ta có:
`{13}/{17}=1- 4/{17}`
`{25}/{29}=1- 4/ {29}`
Vì `17<29=>4/{17}>4/{29}`
`=>1-4/{17}<1- 4/{29}`
Vậy `{13}/{17}<{25}/{29}`
$\\$
`b)` Ta có:
`{7}/{41}=1- {34}/{41}`
`{13}/{47}=1- {34}/ {47}`
Vì `41<47=>{34}/{41}>{34}/{47}`
`=>1-{34}/{41}<1- {34}/{47}`
Vậy `{7}/{41}<{13}/{47}`
$\\$
`c)` Ta có:
`{17}/{42}=1- {25}/{42}`
`{13}/{38}=1- {25}/ {38}`
Vì `42>38=>{25}/{42}<{25}/{38}`
`=>1-{25}/{42}>1- {25}/{38}`
Vậy `{17}/{42}>{13}/{38}`