`(392-x)/32+(390-x)/34+(388-x)/36+(386-x)/38+(384-x)/40=-5`
`⇔(392-x)/32+1+(390-x)/34+1+(388-x)/36+1+(386-x)/38+1+(384-x)/40+1=0`
`⇔(392-x+32)/32+(390-x+34)/34+(388-x+36)/36+(386-x+38)/38+(384-x+40)/40=0`
`⇔(424-x)/32+(424-x)/34+(424-x)/36+(424-x)/38+(424-x)/40=0`
`⇔(424-x).(1/32+1/34+1/36+1/38+1/40)=0`
`⇔424-x=0` (vì `1/32+1/34+1/36+1/38+1/40>0`)
`⇔x=424`
Vậy `S={424}`
