sin, cos, tan, asin, acos, atan, atan2 - trigonometric functions
double atan2(x, y)
double x, y;
Sin, cos and tan return trigonometric functions of radian arguments.
The magnitude of the argument should be checked by the caller to make
sure the result is meaningful.
Asin returns the arc sin in the range -/2 to /2.
Acos returns the arc cosine in the range 0 to .
Atan returns the arc tangent of x in the range -/2 to /2.
Atan2 returns the arc tangent of x/y in the range - to .
Arguments of magnitude greater than 1 cause asin and acos to return
value 0; errno is set to EDOM. The value of tan at its singular points
is a huge number, and errno is set to ERANGE.
The value of tan for arguments greater than about 2**31 is garbage.
19 January 1983 SIN(3M)