30. let {a,} be a sequence of positive real numbers such that a = 1 a+1-22,an+1an o heoo- a all n 21. then, the sum of the series 2-1lies in the interval 0-6 ol

30. Let {a,} be a sequence of positive real numbers such that a = 1 a+1-22,an+1an O heoo- a all n 21. Then, the sum of the series 2-1lies in the interval 0-6 oldsine (d) (4, 5] 3n (a) ( 1,2] (b)(2.3 to (c) (3, 41