acos() and acosf()

  #include <math.h>
  

  double acos(double x);

  

  float  acosf(float x);

  

acos() computes the principal value of the arc cosine of x.

The arc cosine cos^(-1)(x) of x in the range between 0 and Pi if x is in the range -1 <= x <= 1. If x is not in this range, NAN is returned and errno is set to EDOM.

asin() and asinf(),

atan() and atanf(),

atan2() and atan2f(),

cos() and cosf(),

sin() and sinf(), and

tan() and tanf()