# Library Function cos in Math Class

## Library Function cos of math.h Header File in C

On this page we will discuss about library function cos in math class which is used in C.
The C header file math.h contains the standard math library functions that can be used for performing various mathematical operations. The acos function returns the cosine of x in radians.

## Library Function cos in Math class used in C

In C programming language the cos function is included in math.h header file.

The range of input argument which is passed to cos function is not limited here as it can be any value either negative or positive and returns the cosine of parameter x in radians.

### Declaration of cos function

 double cos(double x)

We can find the cosine of different data types like float or long double by using the specific function cosf and cosl respectively.
float cosf(float x);
long double cosl(long double x);


### Parameters of cos function

The x parameter is the angle in radians. The function returns a value of type double, which is the cosine of the angle.

### Return value of cos function

The cos function returns the principal value of cosine of parameter x that has a value between -1 and 1, inclusive and it’s return type is double.

ParameterReturn Value
angle xThis function returns a value that lies in the interval [-1,1].

### Implementation of Library Function math.h cos

#### Example 1:

Run
#include<stdio.h>
#include<conio.h>
#define PI 3.141592654
int main()
{
// Declaring temporary variables
double angle = 4.12345, result;
angle = (angle * PI) / 180;
result = cos(angle);
// Display the result of calculation
printf("cos of %.2lf radian = %.2lf", angle, result);
return 0;
}


#### Output:

cos of 0.07 radian = 1.00


#### Example 2:

Run
#include<stdio.h>
#include<conio.h>
int main() {
printf("The cosine of %lf is %lf \n", 6.5, cos(6.5));
printf("The cosine of %lf is %lf \n", -6.5, cos(-6.5));
//converting the degrees angle into radians and then applying cos()
// degrees = 75.0
// constant  PI = 3.14159265
double answer=cos(75.0 * (3.14159265 / 180.0));
// Displaying the result of calculation
printf("The cosine of %lf is %lf \n", 75.0, answer);
}


#### Output:

The cosine of 6.500000 is 0.976588
The cosine of -6.500000 is 0.976588
The cosine of 75.000000 is 0.258819


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