Giải thích các bước giải:
`M=1/2^2 + 1/4^2 + 1/6^2 + ... + 1/10^2`
`=> M < 1/(1.3) + 1/(3.5) + 1/(5.7) + ... + 1/(9.11)`
`=> M < 1/2 ( 2/(1.3) + 2/(3.5) + 2/(5.7) + ... + 2/(9.11))`
`=> M< 1/2 ( 1 - 1/3 + 1/3 - 1/5 + 1/5 - 1/7 + ... + 1/9 -1/11)`
`=> M < 1/2 ( 1-1/11)`
`=> M < 1/2 - 1/(2.11) < 1/2`
`=> M < 1/2 (1)`
$\\$
`M=1/2^2 + 1/4^2 + 1/6^2 + ... + 1/10^2`
`=> M > 1/(3.5) + 1/(5.7) + 1/(7.9) + ... + 1/(11.13)`
`=> M > 1/2 ( 2/(3.5) + 2/(5.7) + 2/(7.9) + ... + 2/(11.13))`
`=> M > 1/2 (1/3 - 1/5 + 1/5 - 1/7 + 1/7 - 1/9 + ... + 1/11 - 1/13)`
`=> M > 1/2 ( 1/3 - 1/13)`
`=> M > 1/6 - 1/(2.13) = 5/39 > 5/15 = 1/3 (2)`
Từ `(1)` và `(2) => 1/3 < M < 1/2`
