Đáp án:
`A=11/5`
Giải thích các bước giải:
`A=3-1/3-1/6-1/10-1/15-1/21-1/28-1/36-1/45`
`=3-(1/3+1/6+1/10+1/15+1/21+1/28+1/36+1/45)`
`=3-2.(1/6+1/12+1/20+1/30+1/42+1/56+1/72+1/90)`
`=3-2.(1/(2.3)+1/(3.4)+1/(4.5)+1/(5.6)+1/(6.7)+1/(7.8)+1/(8.9)+1/(9.10))`
`=3-2.(1/2-1/3+1/3-1/4+1/4-1/5+1/5-1/6+1/6-1/7+1/7-1/8+1/8-1/9+1/9-1/10)`
`=3-2.(1/2-1/10)`
`=3-2.(5/10-1/10)`
`=3-2.(4)/(10)`
`=3-4/5`
`=15/5-4/5`
`=11/5`
Vậy `A=11/5`
