`(a_1-1)/100=(a_2-2)/99=(a_3-3)/98=...=(a_100-100)/1`
Áp dụng t/c dãy tỉ số = nhau:
`(a_1-1+a_2-2+a_3-3+...+a_(100)-100)/(100+99+...+1)`
`=((a_1+a_2+...+a_(100))-(1+2+...+100))/(100+99+...+1)`
`=(a_1+a_2+...+a_(100))/(100+99+...+1) -1`
`=10100/5050 -1=2-1=1`
Suy ra:
`(a_1-1)/100=1 => a_1-1=100 => a_1=101`
...v.v
`(a_100-100)/1=1 => a_100-100=1 => a_100=101`
`⇒a_1=a_2=...=a_(100)=101`