`Bài   1`

`a)(x-1)/12+(x-1)/20+(x-1)/30+(x-1)/42+(x-1)/56+(x-1)/72=16/9`

`(x-1)(1/(3*4)+1/(4*5)+1/(5*6)+1/(6*7)+1/(7*8)+1/(8*9))=16/9`

`(x-1)*(1/3-1/4+1/4-1/5+.....+1/8-1/9)=16/9`

`(x-1)*(1/3-1/9)=16/9`

`(x-1)*2/9=16/9`

`x-1=8`

`x=9`

` Vậy   x=9`

`b)(x-1)/2024+(x-2)/2025=(x-3)/2026+(x-4)/2027`

`(x-1)/2024+1+(x-2)/2025+1=(x-3)/2026+1+(x-4)/2027+1`

`(x+2023)/2024+(x+2023)/2025=(x+2023)/2026+(x+2023)/2027`

`=>(x+2023)/2024+(x+2023)/2025-(x+2023)/2026-(x+2023)/2027=0`

`=>(x+2023)(1/2024+1/2025-1/2026-1/2027)=0`

`=>x+2023=0 ( vì    1/2024+1/2025-1/2026-1/2027 ne 0)`

`x=-2023`

` Vậy   x=-2023`

`c)(x-2)/995+x/997=(x-1)/996+(x+1)/998`

`(x-2)/995-1+x/997-1=(x-1)/996-1+(x+1)/998-1`

`(x-997)/995+(x-997)/997=(x-997)/996+(x-997)/998`

`=>(x-997)/995+(x-997)/997-(x-997)/996-(x-997)/998=0`

`=>(x-997)(1/995+1/997-1/996-1/998)=0`

`=>x-997=0 ( vì   1/995+1/997-1/996-1/998 ne 0)`

`=>x=997`

` Vậy  x=997`