# tan

## PROLOG



           This manual page is part of the POSIX Programmer's Manual.  The
           Linux implementation of this interface may differ (consult the
           corresponding Linux manual page for details of Linux behavior), or
           the interface may not be implemented on Linux.
    


## NAME



           tan, tanf, tanl — tangent function
    


## SYNOPSIS



           #include <math.h>
    
           double tan(double _x_);
           float tanf(float _x_);
           long double tanl(long double _x_);
    


## DESCRIPTION



           The functionality described on this reference page is aligned with
           the ISO C standard. Any conflict between the requirements
           described here and the ISO C standard is unintentional. This
           volume of POSIX.1‐2017 defers to the ISO C standard.
    
           These functions shall compute the tangent of their argument _x_ ,
           measured in radians.
    
           An application wishing to check for error situations should set
           _errno_ to zero and call _feclearexcept_(FE_ALL_EXCEPT) before calling
           these functions. On return, if _errno_ is non-zero or
           _fetestexcept_(FE_INVALID | FE_DIVBYZERO | FE_OVERFLOW |
           FE_UNDERFLOW) is non-zero, an error has occurred.
    


## RETURN VALUE



           Upon successful completion, these functions shall return the
           tangent of _x_.
    
           If the correct value would cause underflow, and is not
           representable, a range error may occur, and _tan_(), _tanf_(), and
           _tanl_() shall return 0.0, or (if IEC 60559 Floating-Point is not
           supported) an implementation-defined value no greater in magnitude
           than DBL_MIN, FLT_MIN, and LDBL_MIN, respectively.
    
           If _x_ is NaN, a NaN shall be returned.
    
           If _x_ is ±0, _x_ shall be returned.
    
           If _x_ is subnormal, a range error may occur
           and _x_ should be returned.
    
           If _x_ is not returned, _tan_(), _tanf_(), and _tanl_() shall return an
           implementation-defined value no greater in magnitude than DBL_MIN,
           FLT_MIN, and LDBL_MIN, respectively.
    
           If _x_ is ±Inf, a domain error shall occur, and either a NaN (if
           supported), or an implementation-defined value shall be returned.
    
           If the correct value would cause underflow, and is representable,
           a range error may occur and the correct value shall be returned.
    
           If the correct value would cause overflow, a range error shall
           occur and _tan_(), _tanf_(), and _tanl_() shall return ±HUGE_VAL,
           ±HUGE_VALF, and ±HUGE_VALL, respectively, with the same sign as
           the correct value of the function.
    


## ERRORS



           These functions shall fail if:
    
           Domain Error
                       The value of _x_ is ±Inf.
    
                       If the integer expression (_math_errhandling_ &
                       MATH_ERRNO) is non-zero, then _errno_ shall be set to
                       **[EDOM]**.  If the integer expression (_math_errhandling_ &
                       MATH_ERREXCEPT) is non-zero, then the invalid
                       floating-point exception shall be raised.
    
           Range Error The result overflows
    
                       If the integer expression (_math_errhandling_ &
                       MATH_ERRNO) is non-zero, then _errno_ shall be set to
                       **[ERANGE]**.  If the integer expression (_math_errhandling_
                       & MATH_ERREXCEPT) is non-zero, then the overflow
                       floating-point exception shall be raised.
    
           These functions may fail if:
    
           Range Error The result underflows, or the value of _x_ is subnormal.
    
                       If the integer expression (_math_errhandling_ &
                       MATH_ERRNO) is non-zero, then _errno_ shall be set to
                       **[ERANGE]**.  If the integer expression (_math_errhandling_
                       & MATH_ERREXCEPT) is non-zero, then the underflow
                       floating-point exception shall be raised.
    
           _The following sections are informative._
    


## EXAMPLES



       **Taking the Tangent of a 45-Degree Angle**
               #include <math.h>
               ...
               double radians = 45.0 * M_PI / 180;
               double result;
               ...
               result = tan (radians);
    


## APPLICATION USAGE



           There are no known floating-point representations such that for a
           normal argument, _tan_(_x_) is either overflow or underflow.
    
           These functions may lose accuracy when their argument is near a
           multiple of π/2 or is far from 0.0.
    
           On error, the expressions (_math_errhandling_ & MATH_ERRNO) and
           (_math_errhandling_ & MATH_ERREXCEPT) are independent of each other,
           but at least one of them must be non-zero.
    


## RATIONALE



           None.
    


## FUTURE DIRECTIONS



           None.
    


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