atan
From cppreference.com
                    
                                        
                    
                    
                                                            
                    |   Defined in header <math.h>
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|   float       atanf( float arg );  | 
(since C99) | |
|   double      atan( double arg );  | 
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|   long double atanl( long double arg );  | 
(since C99) | |
Computes arc tangent of arg
[edit] Parameters
| arg | - | floating point value | 
[edit] Return value
Arc tangent of arg in radians in the range of [-π/2; π/2] radians.
[edit] See also
|   arc tangent, using signs to determine quadrants   (function)  | |
|    computes arc sine (arcsin(x))  (function)  | |
|   computes arc cosine (arccos(x))   (function)  | |
|    computes tangent (tan(x))  (function)  | |
|   C++ documentation for atan 
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