Tham khảo
` a)` Đặt `\frac{a}{b}=\frac{3}{7}=k(k \ne 0)`
`⇒a=7k,b=3k`
Nên `b-a=60`
`⇒3k-7k=60`
`⇒-4k=60`
`⇒k=-15`
Do đó `a=7.(-15)=-105`
`b=3.(-15)=-45`
Do vậy `\frac{a}{b}=\frac{-105}{-45}`
`b)` Xét hiệu:
`⇒(n^2-2n+5)-n(n-2) \vdots n-2`
`⇒n^2-2n+5-n^2+2n \vdots n-2`
`⇒5 \vdots n-2`
`⇒n-2∈Ư(5)={1,-1,5,-5}`
`⇒n∈{3,1,7,-3}`
`\text{©CBT}`