1、证：an=(9n^2-9n+2)/(9n^2-1)
=(3n-1)(3n-2)/((3n+1)(3n-1))
=(3n-2)/(3n+1)
=1-3/(3n+1)
由an=1-3/(3n+1),可知{an}是递增数列
当n=1时,an=1-3/4=1/4>0
又,3/(3n+1)>0,即,an=1-3/(3n+1)2/3
所以,{an}只有a2=4/7在区间（1/3,2/3）内下一题，谢谢！已补齐