C Language and Libraries Help (clang.hlp) (Table of Contents; Topic list)
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Long Double Trigonometric Functions
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─────Run-Time Library───────────────────────────────────────────────────────
 
  Include:   <math.h>, <errno.h>
 
  Syntax:    long double _acosl( long double x );
             long double _asinl( long double x );
             long double _atanl( long double x );
             long double _atan2l( long double y, long double x );
 
  Returns:   (_acosl) the arccosine result, or 0 if x is greater than 1
                      or less than -1.
             (_asinl) the arcsine result, or 0 if x is greater than 1 or
                      less than -1.
             (_atanl) the arctangent result.
             (_atan2l) the arctangent result, or 0 if both arguments
                      are 0.
             errno: EDOM
 
  See also:  cos, _cosl, sin, _sinl, tan, _tanl, _matherrl
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