Question

[Hoai Bao Tran]

CMR":

\(\dfrac{1}{3}\cdot\dfrac{4}{6}\cdot\dfrac{7}{9}\cdot.......\cdot\dfrac{\left(3n-2\right)}{3n}\cdot\dfrac{\left(3n+1\right)}{3n+3}< \dfrac{1}{3\sqrt{n+1}}\)