Giải:
`A = 1/4 + 1/9 + 1/16 + ... + 1/81 + 1/100`
`→ A = 1/(2 . 2) + 1/(3 . 3) + 1/(4 . 4) + ... + 1/(9 . 9) + 1/(10 . 10)`
`→ A > 1/(2 . 2) + 1/(3 . 4) + 1/(4 . 5) + ... + 1/(9 . 10) + 1/(10 . 11)`
`→ A > 1/4 + 1/3 - 1/4 + 1/4 - 1/5 + ... + 1/9 - 1/10 + 1/10 - 1/11`
`→ A > 1/4 + 1/3 - 1/11 = (33 + 44 - 12)/132 = 65/132` (đpcm)