std::sqrt
From cppreference.com
                    
                                        
                    
                    
                                                            
                    |   Defined in header <cmath>
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|   float       sqrt( float arg );  | 
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|   double      sqrt( double arg );  | 
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|   long double sqrt( long double arg );  | 
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|   double      sqrt( Integral arg );  | 
(since C++11) | |
Computes square root of arg.
[edit] Parameters
| arg | - | floating point or integer value | 
[edit] Return value
square root of arg.
Domain error occurs if arg is negative. NAN is returned in that case.
[edit] See also
|    (C++11)  | 
   computes cubic root  (3√x)   (function)  | 
|    raises a number to the given power (xy)   (function)  | |
|    complex square root in the range of the right half-plane   (function template)  | |
|    applies the function std::sqrt to each element of valarray   (function template)  | |