Question

How to use acos() function to get the arc cosine value of N in C

Answer 1

#include <stdio.h>     
#include <math.h>
 
int main()
{
    printf("acos(0) = %f\n", acos(0));
    printf("acos(-1) = %f\n", acos(-1));
    printf("acos(1) = %f\n", acos(1));
    printf("acos(0.5) = %f\n", acos(0.5));
  
    double ac = acos(.9);
    printf("acos(0.9) = %.6f\n", ac);
 
    return 0;
}

 
/*
run:

acos(0) = 1.570796
acos(-1) = 3.141593
acos(1) = 0.000000
acos(0.5) = 1.047198
acos(0.9) = 0.451027
 
*/

 

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Answer 2

#include <stdio.h>
#include <math.h>
#include <errno.h>
#include <fenv.h>

#pragma STDC FENV_ACCESS ON

int main(void)
{
    printf("acos(-1) = %f\n", acos(-1));
    printf("acos(0.0) = %f 2 * acos(0.0) = %f\n", acos(0), 2 * acos(0));
    printf("acos(0.5) = %f 3 * acos(0.5) = %f\n", acos(0.5), 3 * acos(0.5));
    printf("acos(1) = %f\n\n", acos(1));
   
    errno = 0; 
    feclearexcept(FE_ALL_EXCEPT);
    printf("acos(1.1) = %f\n", acos(1.1));
    if (errno == EDOM) {
        perror("    errno == EDOM");
    }
    if (fetestexcept(FE_INVALID)) {
        puts("    FE_INVALID raised");
    }
}


 
/*
run:
   
acos(-1) = 3.141593
acos(0.0) = 1.570796 2 * acos(0.0) = 3.141593
acos(0.5) = 1.047198 3 * acos(0.5) = 3.141593
acos(1) = 0.000000

acos(1.1) = nan
    errno == EDOM: Numerical argument out of domain
    FE_INVALID raised
  
*/

 

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