$\displaystyle Problem$ $\displaystyle 3$

Assume $\displaystyle \sum_{n=1}^{\infty}\frac{a_{n}}{\sqrt{n}}$ converges

where $\displaystyle a_{n}>0$ and $\displaystyle a_{n}\geq a_{n+1}$ for $\displaystyle \forall$ $\displaystyle n \in \mathbb{N}^+$

show that: $\displaystyle \sum_{n=1}^{\infty}a_{n}^2$ converges