Đáp án:
`Q>1/2`
Giải thích các bước giải:
`Q=(1-1/2^2).(1-1/3^2).` `...` `.(1-1/40^2)`
`=>Q=3/2^2. 8/3^2.` `...` `. 1599/40^2`
`=>Q=1.3/2.2. 2.4/3.3.` `...` `. 39.41/40.40`
`=>Q=(1.2...39)/(2.3...40).(3.4...41)/(2.3...40)`
`=>Q=1/40. 41/2`
`=>Q=41/80>40/80=1/2`
Vậy `Q>1/2`.