(根号下n+1-根号n)(根号下n+1+根号n)=1∴根号下n+1-根号n=1/(根号下n+1+根号n)(根号n-根号下n-1)(根号n+根号下n-1)=1∴根号n-根号下n-1=1/(根号n+根号下n-1)∴根号下n+1+根号n>根号n+根号下n-1>0∴1/(根号下n+1+根号n)<1/(根号n+根号下n-1)即:根号下n+1-根号n < 根号n-根号下n-1