1/4 = 1/(2.2) < 1/(1.2) = 1/2 - 1/4
1/16 < 1/(2.4) = 1/4 - 1/8
1/36 < 1/(4.6) = 1/8 - 1/12
1/64 < 1/(6.8) = 1/12 - 1/16
1/100 < 1/(8.10) = 1/16 - 1/20
1/144 < 1/(10.12) = 1/20 - 1/24
1/196 < 1/(12.14) = 1/24 - 1/28
1/256 < 1/(14.16) = 1/28 - 1/32
1/324 < 1/(16.18) = 1/32 - 1/36
⇒ 1/4 + 1/16 + ......+ 1/100 + 1/144 + 1/196 +1/256+1/324< 1/2 - 1/36 < 1/2
(đpcm)