sin, cos, tan, asin, acos, atan, atan2 - trigonometric functions
and their inverses

#include <math.h>

double sin(x)
double x;

double cos(x)
double x;

double tan(x)
double x;

double asin(x)
double x;

double acos(x)
double x;

double atan(x)
double x;

double atan2(y,x)
double y,x;

Sin, cos and tan return trigonometric functions of radian arguments

Asin returns the arc sine in the range -pi/2 to pi/2.

Acos returns the arc cosine in the range 0 to pi.

Atan returns the arc tangent in the range -pi/2 to pi/2.

hypot(x,y) and atan2(y,x) convert from rectangular (x,y) to polar
(r,theta) coordinates that must satisfy x = r*cos theta and y =
r*sin theta.
atan2(y,x) := sign(y)*atan(y/x) if x > 0,
sign(y)*(pi - atan(|y/x|)) if x < 0,
0 if x = y = 0, or
sign(y)*pi/2 if x = 0 != y.

sin(+-INF), cos(+-INF), tan(+-INF), or asin(x) or acos(x) where |x|
> 1, return NaN.

libm(3), hypot(3), sqrt(3)

Robert P. Corbett, W. Kahan, Stuart I. McDonald, Peter Tang and,
for the codes for IEEE 754, Dr. Kwok-Choi Ng.