Calculates the inverse cosine of a number

#include <math.h>
double acos ( double x  );
float acosf ( float x  );         (C99)
long double acosl ( long double x  );         (C99)

acos( ) implements the inverse cosine function, commonly called arc cosine. The argument x must be between -1 and 1, inclusive: -1 x 1. If x is outside the function's domainthat is, greater than 1 or less than -1the function incurs a domain error.

The return value is given in radians, and is thus in the range 0 acos(x) p.

Example

/*
 * Calculate the pitch of a roof given
 * the sloping width from eaves to ridge and
 * the horizontal width of the floor below it.
 */
#define PI 3.141593
#define DEG_PER_RAD (180.0/PI)

double floor_width = 30.0;
double roof_width = 34.6;

double roof_pitch = acos( floor_width / roof_width ) * DEG_PER_RAD ;
printf( "The pitch of the roof is %2.0f degrees.\n", roof_pitch );

This code produces the following output:

The pitch of the roof is 30 degrees.

See Also

The arc cosine functions for complex numbers: cacos( ), cacosf( ), and cacosl( )