Functions HI-TECH C ACOS
ACOS, ASIN, ATAN, ATAN2
#include <math.h> double acos(double f) double asin(double f) double atan(double f) double atan2(double x, double y)
These functions are the converse of the trignometric functions cos, sin and tan. Acos and asin are undefined for arguments whose absolute value is greater than 1.0. The returned value is in radians, and always in the range -pi/2 to +pi/2, except for cos(), which returns a value in the range 0 to pi. Atan2() returns the inverse tan of x/y but uses the signs of its arguments to return a value in the range -pi to +pi.
sin, cos, tan