`B= 1/(2^2) + 1/(3^2) + 1/(4^2)+...+ 1/(100^2)`
$\text{Ta có}$
`1/(2^2) < 1/(1.2)`
`1/(3^2) < 1/(2.3)`
`1/(4^2) < 1/(3.4)`
`...`
`1/(100^2) < 1/(99.100)`
`=> B < 1/(1.2) + 1/(2.3) + ... + 1/(99.100)`
`=> B < 1/1 - 1/2 + 1/2 - 1/3 +...+ 1/99 - 1/100`
`=> B < 1/1 - 1/100`
`=> B < 99/100`
$\text{mà}$ `99/100 < 1`
`=> B <1 (đpcm)`
$\text{TEAM_IQ_2000}$