Để `\frac{2x-1}{x-1}` tối giản
Gọi `d` `∈` `Ư` ( `2x-1`, `x-1` )
`⇒` $\left \{ {{2x-1 d} \atop {x-1\vdots d}} \right.$
`⇒` $\left \{ {{1.(2x-1)\vdots d} \atop {2.(x-1)\vdots d}} \right.$
`⇒` `(2x-2)-(2x-1)`
`⇒` `1` `\vdots` `d`
`⇒` `d` `∈` `Ư(1)=1`
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