#include <math.h>
float tanf(float x);
tanf returns the radian circular tangent of x.
If |x| > 10^9, errno is set to EDOM and tanf returns HUGE_VALF.
If x is NaN, tanf returns x.
If |x| is ?, tanf returns NaN with invalid signal.
tanf conforms to ISO/IEC 9899:1990 (C90) and ISO/IEC 9899:1999 (C99).