Expansion of limit term

[dannee]

Homework Statement

i added a photo of a move of limit of function.
can anyone please explain this move ? step by step.. i can't understand it
thanks in advance !

Homework Equations

The Attempt at a Solution

 

[spamiam]

Do you know what a conjugate is? Try multiplying the numerator and denominator by the conjugate of $\sqrt{x^2 + \frac{1}{n}} - x$.

 

[dannee]

thanks !