`a,(28/2017+20/2019-16/2021)x=98/4034+70/4038-56/4042`
`⇒(28/2017+20/2019-16/2021)x=49/4034+35/4038-28/4042`
`⇒(28/2017+20/2019-16/2021)x=49/2017+35/2019-28/2021`
`⇒(7/2017+5/2019-4/2021)4x=(7/2017+5/2019-4/2021)7`
`⇒4x=7`
`⇒x=7/4`
`b,` Gọi `ƯCLN(3n+2;2n+1)=d`
$⇒\begin{cases}3n+2⋮d⇒2(3n+2)⋮d⇒6n+4⋮d\\2n+1⋮d⇒3(2n+1)⋮d⇒6n+3⋮d\end{cases}$
$⇒(6n+4)-(6n+3)⋮d$
$⇒6n+4-6n-3⋮d$
$⇒(6n-6n)+(4-3)⋮d$
$⇒1⋮d$
$⇒d=1$
`⇒{3n+2}/{2n+1}` là phân số tối giản $(đpcm)$