#include <cmath> double cos( double arg );
The cos() function returns the cosine of arg, where arg is expressed in radians. The return value of cos() is in the range [-1,1]. If arg is infinite, cos() will return NAN and raise a floating-point exception.
C++ also provides the following overloaded forms:
#include <cmath> float cos( float arg ); // same as cosf() in C99 long double cos( long double arg ); // same as cosl() in C99