atan() and atanf()

  #include <math.h>

  

  double atan (double x);

  

  float  atanf(float x);

  

atan() computes the principal value of the arc tangent of x.

The arc tangent tan^(-1)(x), in the range from -Pi/2 to Pi/2 radian

acos() and acosf(),

asin() and asinf(),

atan2() and atan2f(),

cos() and cosf(),

sin() and sinf(), and

tan() and tanf()