acosh

acos

#include <math.h>float acosf(float arg);double acos(double arg); long double acosl(long double arg);

acosf( ) and acosl( ) were added by C99.

The acos( ) family of functions returns the arc cosine of arg. The argument must be in the range –1 to 1; otherwise, a domain error will occur.

Related functions are asin( ), atan( ), atan2( ), sin( ), cos( ), tan( ), sinh( ), cosh( ), and tanh( ).