#include <cmath> double tan( double arg );
The tan() function returns the tangent of arg, where arg is given in radians. If arg is infinite, tan() will return NAN and raise a floating-point exception.
C++ also provides the following overloaded forms:
#include <cmath> float tan( float arg ); // same as tanf() in C99 long double tan( long double arg ); // same as tanl() in C99