1/根号2+1+(1/根号3+根号2)+(1/根号4+根号3)+(1/根号5+根号4)+····+(1/根号10+根号9)
=根号2-1+根号3-根号2+根号4-根号3+根号5-根号4+····+根号10-根号9
=根号10-1