`8`
`1/(100.99)-1/(99.98)-...-1/(3.2)-1/(2.1)`
`=1/(100.99)-(1/(99.98)+...+1/(3.2)+1/(2.1))`
`=1/(99)-1/(100)-(1/(98)-1/(99)+...+1/2-1/3+1-1/2)`
`=1/(99)-1/(100)-(1-1/(99))`
`=1/(99)-1/(100)-1+1/(99)`
`=(1/(99)+1/(99))+(-1/(100)-1)`
`=2/(99)-101/(100)`
`=-9799/9900`
`9`
`1/2x+3/5x=-33/10`
`(1/2+3/5)x=-33/10`
`11/10 . x=-33/10`
`x=(-33/10) : 11/10`
`x=(-33/10) . 10/11`
`x=-3`
Vậy `x=-3`
`10`
`(x+5)/(2005)+(x+6)/(2004)+(x+7)/(2003)=-3`
`((x+5)/(2005)+1)+((x+6)/(2004)+1)+((x+7)/(2003)+1)=0`
`(x+2010)/(2005)+(x+2010)/(2004)+(x+2010)/(2003)=0`
`(x+2010).(1/(2005)+1/(2004)+1/(2003))=0`
`x+2010=0(1/(2005)+1/(2004)+1/(2003)\ne 0)`
`x=0-2010`
`x=-2010`
Vậy `x=-2010`
