# C cos()

The cos() function defined in the math.h header file. It helps to return the cosine value of the given radian value.

``````
double cos(double x); #where x can be in int, float or long double
```
```

Also, two functions cosf() and cosl() were used with type float and long double respectively.

``````
float cosf(float x);
long double cosl(long double x);
```
```

## cos() Parameters:

The cos() function takes a single parameter which is a value representing an angle expressed in radians.

Parameter Description Required / Optional
double value A double value indicates angle in radians Required

## cos() Return Value

The return value of cos() function is a number between 1 and -1.

Input Return Value
-1<x ≥ 1 a number greater than or equal to 0
x < -1 NaN (not a number)

## Examples of cos()

### Example 1: Working of cos() function in C?

``````
#include <stdio.h>
#include <math.h>
#define PI 3.14159265

int main () {
double v, out, value;

v = 60.0;
value = PI / 180.0;
out = cos( v*value );
printf("Cosine value of %lf is %lf degrees\n", v, out);

v = 90.0;
value = PI / 180.0;
out = cos( v*value );
printf("Cosine value of %lf is %lf degrees\n", v, out);

return(0);
}
```
```

Output:

```
Cosine value of 60.000000 is 0.500000 degrees
Cosine value of 90.000000 is 0.000000 degrees
```

### Example 2: How cos() function works in C?

``````
#include <stdio.h>
#include <math.h>
#define PI 3.14159265

int main()
{
double pr = 30, output;

pr = (pr * PI) / 180;
output = cos(pr);

printf("The cos value of %.2lf radian = %.2lf", pr, output);

return 0;
}
```
```

Output:

```
The cos value of 0.52 radian = 0.87
```
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