Đáp án:
Nếu là `2/31.33` thì `B=32/33`
Nếu là `2/33.35` thì `B=34/35`
Nếu là `2/3135` thì `B=56/57`
Giải thích các bước giải:
Nếu là `2/31.33`
`B=2/3+2/15+2/35+...+2/31.33`
`B=2/1.3+2/3.5+2/5.7+...+2/31.33`
`B=1/1-1/3+1/3-1/5+...+1/31-1/33`
`B=1/1-1/33=33/33-1/33=32/33`
Nếu là `2/33.35`
`B=2/3+2/15+2/35+...+2/33.35`
`B=2/1.3+2/3.5+2/5.7+...+2/33.35`
`B=1/1-1/3+1/3-1/5+...+1/33-1/35`
`B=1/1-1/35=35/35-1/35=34/35`
Nếu là `2/3135`
`B=2/3+2/15+2/35+...+2/3135`
`B=2/1.3+2/3.5+2/5.7+...+2/55.57`
`B=1/1-1/3+1/3-1/5+...+1/55-1/57`
`B=1/1-1/57=57/57-1/57=56/57`
