I need to prove that 
 $$ \lim\_{n\to+\infty}\cos{\big{(}\pi \sqrt{n^2+n}\big{)}}=1$$

But this is something that seems highly unlikely to have a limit, but I am probably wrong. Wolfram Alpha says "$0$ to $1$". What does that even mean? How to prove this?

If you could provide only a hint (if this limit exists) so I can finish the task myself.