1/2+1/6+1/12+1/20+1/30+1/42
=1-1/2+1/2-1/3+1/3-1/4+1/4-1/5+1/5-1/6+1/6-1/7
=1-1/7
=6/7
如果本题有什么不明白可以追问,有什么规律，用文字说明一下1/2=1/1x2=1-1/21/6=1/2x3=1/2-1/3