Đáp án:
Giải thích các bước giải:
`1)A=(1 -1/2).(1 -1/3).(1-1/4)`
`A=1/2 . 2/3 .3/4`
`A=1/4`
`2)`
`a)B=1/2^2 +1/3^2+1/4^2+...+1/201^2`
`B=1/2.2 +1/3.3 +1/4.4 +...+1/201.201`
`B<1/1.2 +1/2.3 +1/3.4 +...+1/200.201`
`A<1 -1/2+1/2-1/3+1/3-1/4+...+1/200-1/201`
`A<1-1/201<1`
`=>A<1`
`b)C = 3/2.5 + 3/5.8 + 3/8.11 + 3/11.14 + 3/14.17`
`C=1/2-1/5+1/5-1/8+1/8-1/11+1/11-1/14+1/14-1/17`
`C=1/2-1/17<1/2`
`=>C<1/2`