# C library function - asin()

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## Description

The C library function double asin(double x) returns the arc sine of x in radians.

## Declaration

Following is the declaration for asin() function.

```double asin(double x)
```

## Parameters

• x − This is the floating point value in the interval [-1,+1].

## Return Value

This function returns the arc sine of x, in the interval [-pi/2,+pi/2] radians.

## Example

The following example shows the usage of asin() function.

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

#define PI 3.14159265

int main () {
double x, ret, val;
x = 0.9;
val = 180.0 / PI;

ret = asin(x) * val;
printf("The arc sine of %lf is %lf degrees", x, ret);

return(0);
}
```

Let us compile and run the above program that will produce the following result −

```The arc sine of 0.900000 is 64.158067 degrees
```
math_h.htm