Đáp án:
`A<1/2`
Giải thích các bước giải:
`A=1/2^2+1/4^2+1/6^2+...+1/100^2`
`=>A=1/2.2+1/4.4+1/6.6+...+1/100.100`
`=>A<1/4+1/2.4+1/4.6+...+1/98.100`
`=>A<1/4+1/2(2/2.4+2/4.6+...+1/98.100)`
`=>A<1/4+1/2(1/2-1/4+1/4-1/6+...+1/98-1/100)`
`=>A<1/4+1/2(1/2-1/100)`
`=>A<1/4+1/2*49/100`
`=>A<1/4+49/200`
`=>A<99/200<1/2`
`=>A<1/2`
Vậy `A<1/2`.