This manual page is part of the POSIX Programmer's Manual. The Linux implementation of this interface

       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.

       Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1-2017, Standard
       for  Information  Technology  --  Portable  Operating  System  Interface  (POSIX),  The  Open  Group Base
       Specifications Issue 7, 2018 Edition, Copyright (C) 2018 by the Institute of Electrical  and  Electronics
       Engineers, Inc and The Open Group.  In the event of any discrepancy between this version and the original
       IEEE  and The Open Group Standard, the original IEEE and The Open Group Standard is the referee document.
       The original Standard can be obtained online at http://www.opengroup.org/unix/online.html .

       Any typographical or formatting errors that appear in this page are most likely to have  been  introduced
       during   the   conversion  of  the  source  files  to  man  page  format.  To  report  such  errors,  see
       https://www.kernel.org/doc/man-pages/reporting_bugs.html .

IEEE/The Open Group                                   2017                                           TAN(3POSIX)

       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.

       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.

       Thefollowingsectionsareinformative.

TakingtheTangentofa45-DegreeAngle
           #include <math.h>
           ...
           double radians = 45.0 * M_PI / 180;
           double result;
           ...
           result = tan (radians);

       None.

       tan, tanf, tanl — tangent function

       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.

       None.

       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.

atan(), feclearexcept(), fetestexcept(), isnan()

       The Base Definitions volume of POSIX.1‐2017, Section4.20, TreatmentofErrorConditionsforMathematicalFunctions, <math.h>

       #include <math.h>

       double tan(double x);
       float tanf(float x);
       long double tanl(long double x);