By use of the Squeeze Theorem calculate the limit $ \lim\limits_{n \to \infty } \frac{1}{\sqrt{n^2+1}} + \frac{1}{\sqrt{n^2+2}} + \frac{1}{\sqrt{n^2+n}} $.
By use of the Squeeze Theorem calculate the limit $ \lim\limits_{n \to \infty } \frac{1}{\sqrt{n^2+1}} + \frac{1}{\sqrt{n^2+2}} + \frac{1}{\sqrt{n^2+n}} $.