Number Theory Doubt

Hi Experts,

I am having a hard time understanding the concept that is mentioned in the GmatClub book.

Pardon my ignorance; Here is the doubt

Its been mentioned that

\sqrt{x^2}=|x| ----(1)

Then, Why
\sqrt{25}=5 Not|5| . It can be assumed that x = 5 and putting it in equation 1

\sqrt{5^2} =|5|

Or is the equation is valid only for variables not for any numbers. Please help in clarifying this concept.

Your help will be appreciated.

Thanks