`Q = 1/6^2 + 1/8^2 + ... + 1/100^2`
`Q = 1/(6.6) + 1/(8.8) + ... + 1/(100.100) < 1/(4.6) + 1/(6.8) + ... + 1/(98.100)`
`Q = 1/(6.6) + 1/(8.8) + ... + 1/(100.100) < ( 2/(4.6) + 2/(6.8) + ... + 2/(98.100) ) . 1/2`
`Q = 1/(6.6) + 1/(8.8) + ... + 1/(100.100) < ( 1/4 - 1/6 + 1/6 - 1/8 + ... + 1/98 - 1/100 ) . 1/2`
`Q = 1/(6.6) + 1/(8.8) + ... + 1/(100.100) < ( 1/4 - 1/100 ) . 1/2`
`Q = 1/(6.6) + 1/(8.8) + ... + 1/(100.100) < 6/25 . 1/2`
`Q = 1/(6.6) + 1/(8.8) + ... + 1/(100.100) < 3/25 `
Mà `Q < 3/25 ; 3/25 < 1/6 ⇒ Q < 1/6` ( Điều phải chứng minh )
