Đáp án + Giải thích các bước giải:
`N=3/2-5/6+7/12-9/20+11/30-13/42+15/56`
`=(1+2)/2 - (2+3)/6 + (3+4)/12 - (4+5)/20 + (5+6)/30 - (6+7)/42 + (7+8)/56`
`= 1/2 + 2/2 - (2/6+3/6)+3/12+4/12-(4/20+5/20)+(5/30+6/30)-(6/42+7/42)+7/56+8/56`
`=1/2+1-(1/3+1/2)+1/4+1/3-(1/5+1/4)+(1/6+1/5)-(1/7+1/6)+1/8+1/7`
`=1+1/2-1/3-1/2+1/4+1/3-1/5-1/4+1/6+1/5-1/7-1/6+1/8+1/7`
`=1+(1/2-1/2)+(1/3-1/3)+(1/4-1/4)+(1/5-1/5)+(1/6-1/6)+(1/7-1/7)+1/8`
`=1+1/8=9/8`
