Đáp án + Giải thích các bước giải:
`2/3+2/15+2/35+2/63+2/99`
`=2xx(1/3+1/15+1/35+1/63+1/99)`
`=2xx(1/(1xx3)+1/(3xx5)+1/(5xx7)+1/(7xx9)+1/(9xx11))`
`=2xx1/2xx(2/(1xx3)+2/(3xx5)+2/(5xx7)+2/(7xx9)+2/(9xx11))`
`=1-1/3+1/3-1/5+1/5-1/7+1/7-1/9+1/9-1/11`
`=1-1/11`
`=11/11-1/11`
`=10/11`