1/2+1/6+1/12+1/20+······+1/72+1/90）（计算）

1/2+1/6+1/12+1/20+······+1/72+1/90）
=(1-1/2)+(1/2-1/3)+(1/3-1/4)+.+(1/9-1/10)
=1-1/2+1/2-1/3+1/3-1/4+.+1/9-1/10
=1-1/10
=9/10;
如果本题有什么不明白可以追问,