Factor 999 into its prime factors

           999 = 3³ • 37 

To simplify a square root, we extract factors which are squares, i.e., factors that are raised to an even exponent.

Factors which will be extracted are :

           9 = 3² 

Factors which will remain inside the root are :

           111 = 3 • 37 

To complete the simplification we take the squre root of the factors which are to be extracted. We do this by dividing their exponents by 2 :

           3 = 3 

The simplified SQRT looks like this: 

         3 • sqrt (111)