3AnA(n+1)=An-A(n+1)两边同除以AnA(n+1)1/A(n+1)-1/An=3所以{1/an}是公差为3的等差数列首项=1/a1=2所以1/an=2+3(n-1)=3n-1故通项公式an=1/(3n-1)
