`(x+1)/(2000)+(x+2)/(1999)+(x+3)/(1998)=(x+4)/(1997)+(x+5)/(1996)+(x+6)/(1995)`
`<=>((x+1)/(2000)+1)+((x+2)/(1999)+1)+((x+3)/(1998)+1)=((x+4)/(1997)+1)+((x+5)/(1996)+1)+((x+6)/(1995)+1)`
`<=>((x+1)/(2000)+(2000)/(2000))+((x+2)/(1999)+(1999)/(1999))+((x+3)/(1998)+(1998)/(1998))=((x+4)/(1997)+(1997)/(1997))+((x+5)/(1996)+(1996)/(1996))+((x+6)/(1995)+(1995)/(1995))`
`<=>(x+1+2000)/(2000)+(x+2+1999)/(1999)+(x+3+1998)/(1998)=(x+4+1997)/(1997)+(x+5+1996)/(1996)+(x+6+1995)/(1995)`
`<=>(x+2001)/(2000)+(x+2001)/(1999)+(x+2001)/(1998)=(x+2001)/(1997)+(x+2001)/(1996)+(x+2001)/(1995)`
`<=>(x+2001)/(2000)+(x+2001)/(1999)+(x+2001)/(1998)-(x+2001)/(1997)-(x+2001)/(1996)-(x+2001)/(1995)=0`
`<=>(x+2001)((1)/(2000)+(1)/(1999)+(1)/(1998)-(1)/(1997)-(1)/(1996)-(1)/(1995))=0`
`<=>x+2001=0`
Vì `(1)/(2000)+(1)/(1999)+(1)/(1998)-(1)/(1997)-(1)/(1996)-(1)/(1995)\ne0`
`<=>x=-2001`
Vậy `S={-2001}`
