Đáp án + Giải thích các bước giải:
`E=3/(6.8)+3/(8.10)+...+3/(98.100)`
`=3/2 . (2/(6.8)+2/(8.10)+...+2/(98.100) )`
`=3/2 . (1/6-1/8+1/8-1/10+...+1/98-1/100)`
`=3/2 . (1/6-1/100)=47/200`
`F=1/6+1/12+1/20+...+1/90`
`=1/(2.3)+1/(3.4)+1/(4.5)+...+1/(9.10)`
`=1/2-1/3+1/3-1/4+1/4-1/5+...+1/9-1/10`
`=1/2-1/10=2/5`