#include <math.h>float tanf(float arg);double tan(double arg); long double tanl(long double arg);
tanf( ) and tanl( ) were added by C99.
The tan( ) family of functions returns the tangent of arg. The value of arg must be in radians.
Related functions are acos( ), asin( ), atan( ), atan2( ), cos( ), sin( ), sinh( ), cosh( ), and tanh( ).