C library - asin() function

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The C math library asin() function is used to returns the arcsine (inverse sine) of passed 'arg' in radians in the range [−π/2, π/2].

The inverse sine, also known as the arcsine. It is the inverse of the sine function, which reverses the sine function's effect. It is denoted as sin⁻¹(x) or asin(x).

For a given value 'arg' in the range [−1, 1], the inverse sine function sin⁻¹(arg) returns the angle θ in the range [−π/2, π/2].

Syntax

Following is the syntax of the C asin() function −

double asin( double arg );

Parameters

This function accepts a single parameter −

• arg − It is the argument for which arcsine is to be calculated. It will be type double and should be within the range [-1, 1].

Return Value

If no errors occur, the arc sine of the argument (arg) is returned in the range [-π/2, +π/2] in radians.

Example 1

Following is the basic c program to demonstrate the use of asin() to obtain an angle in radians.

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

int main() {
   double arg = 1.0;
   double res = asin(arg);
   printf("The arc sine of %f is %f radians.\n", arg, res);
   return 0;
}

Output

Following is the output −

The arc sine of 1.000000 is 1.570796 radians.

Example 2

Let's create another example, we use the asin() function to obtain the inverse sine value in radian, then after in degree.

#include <stdlib.h>
#include <stdio.h>
#include <math.h>
#define PI 3.14159265
int main() {
   double k = 0.5;
   double res = asin(k);
   // Convert radians to degrees
   double val = (res * 180) / PI; 
   printf("The arcsine of %f is %f radians or degree %f degree. \n", k, res, val);
   return 0;
}

Output

Following is the output −

The arcsine of 0.500000 is 0.523599 radians or degree 30.000000 degree.

Example 3

Now, Create another c program to display the value of the arcsine. If the 'k' lies between -1 to 1 then display the arcsine value, otherwise Invalid input!

#include <stdio.h>
#include <math.h>
#define PI 3.14159265
int main() {
   double k = -5.0;
   if (k >= -1.0 && k <= 1.0) {
      double res = asin(k);
      double val_degrees = (res * 180.0) / PI;
      printf("The arcsine of %.2f is %.6f radians or %.6f degrees\n", k, res, val_degrees);
   } else {
      printf("Invalid input! The value must be between -1 and 1.\n");
   }
   return 0;
}

Output

Following is the output −

Invalid input! The value must be between -1 and 1.