Đáp án:
Giải thích các bước giải:
Bài 10:
`A=(1/2-1).(1/3-1)......(1/10-1)`
`A=-(1/2 . 2/3 ......... 9/10)`
`A=-((1.2..........9)/(2.3...........10))`
`A=-1/10 = -9/90 > -10/90 = -1/9`
`-> A=-1/10 > -1/9`
`-> A > -1/9`
Bài 11:
`B=(1/4-1).(1/9-1).........(1/100-1)`
`B=-(3/4 . 8/9 ....... 99/100 )`
`B=-((1.3)/2^2 . (2.4)/3^2 ....... (9.11)/10^2 )`
`B=-((1.2........9)/(2.3.......10) . (3.4........11)/(2.3.......10) )`
`B=-(1/10 . 11/2 )`
`B=-11/20 < -11/21`
`-> B < -11/21`
`#Dung09`
