# C math library function asin()

In this article, you will learn about C math library function `asin()` that returns arc sine value, with explanation and example.

`asin()` is the standard C math library function that is defined in math library `math.h`.

``#include<math.h>``

## Function prototype of C math library function asin()

``double asin( double x );``

where,

x = floating point value between 1 and -1 (1 >= x >= -1).

### Return Value of asin()

This function returns the arc sine (inverse sine) in radians of `x` that ranges in the interval [ -pi / 2, +pi / 2 ].

Note: `asin()` takes argument between 1 and -1 because the value of sine is in the range of 1 and -1.

## Example: Program to demonstrate the use of C math library function asin()

``````/*Use of math library function asin*/

#include<stdio.h>
#include<math.h>
#define PI 3.1415926

int main()
{
double x, y;

x = 0.5;
y = -0.5;

printf("asin(%.2lf) = %.2lf (radians)\n\n", x, asin( x ));

//calculation arc sine in degrees
printf("asin(%.2lf) = %.2lf (degree)\n\n", x, asin( x ) * 180 / PI );

printf("asin(%.2lf) = %.2lf (radians)\n\n", y, asin( y ));

//calculation arc sine in degrees
printf("asin(%.2lf) = %.2lf (degree)\n", y, asin( y ) * 180 / PI );

return 0;
}
``````

Output

Explanation

In the above program, we have calculated the arc sine of `x` and `y` in radian and degree.

We have defined macro `PI` for representing the value of `pi`.