2.10.94 Number series

Condition: Examine sequences for boundedness above, below, in general (indicate numbers if the sequence is bounded) and for monotonicity (increasing, decreasing, non-increasing, non-decreasing), justify the answer. a) \( a_{n}=\frac{2}{\log _{2}(2 n+1)} \) b) \( a_{n}=\sqrt{n-1} \) c) \( a_{n}=\frac{3}{2+n^{2}} \) d) \( a_{n}=\frac{(-1)^{n+1}}{3} \)