`\text{Cách 1 : Quy đồng tử số}`
$\text{Ta có:}$
`-12/19 = -12/19 ; -4/17 = {-4 .3}/{17.3} = -12/51`
$\text{Vì}$ `19 < 51` $\text{nên}$ `-12/19 < -12/51`
`=> -12/19 < -4/17`
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`\text{Cách 2 : Nhân chéo}`
`-12 . 17 \text{và} -4 . 19`
`-204 \text{và} -76`
`\text{Vì} -204 < - 76` $\text{nên}$ `-12/19 < -4/17`
$\text{Vậy}$ `-12/19 < -4/17`